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 Report No. 2^6 
 
 COO-1U69-0069 
 
 AN ANALOG INPUT/OUTPUT SYSTEM FOR THE ILLIAC II 
 
 by 
 
 Alton Benjamin Otis, Jr. 
 
 September 22, 1967 
 
Report No. 2h6 
 AN ANALOG INPUT/OUTPUT SYSTEM FOR THE ILLIAC II* 
 
 by 
 
 Alton Benjamin Otis, Jr. 
 
 September 22, 196? 
 
 Department of Computer Science 
 University of Illinois 
 Urbana, Illinois 6l801 
 
 * This work was supported in part by Contract No. US AEC AT ( 11-1 ) 1U69 
 and was submitted in partial fulfillment of the requirements for 
 the degree of Master of Science in Electrical Engineering, August, 1967 
 
Ill 
 
 TA3LE OF CONTENTS 
 
 Page 
 
 Z . INTRODUCTION 1 
 
 II. A DESCRIPTION OF THE ILLIAG II ANALOG 
 
 I/O SYSTEM 12 
 
 III. TWO EXAMPLES OF USAGE OF THE ILLIAC II 
 
 ANALOG I/O FACILITY 26 
 
 APPENDIX A. THE ANALOG I/O INTERFACE: EQUIPMENT, 
 
 SIGNAL, AND LOGIC DESCRIPTIONS 38 
 
 APPENDIX 3. THE ANALOG I/O INTERFACE: MACHINE 
 
 LANGUAGE PROGRAM CONTROL. 4 7 
 
 APPENDIX C. ADSYS2 TAPE FORMAT AND COMMAND 
 
 LANGUAGE DESCRIPTIONS 5 3 
 
 APPENDIX D. ADPAK2 SUBROUTINE CALLING SEQUENCES 64 
 
 BLIOGRAPHY 72 
 
IV 
 
 LIST OF FIGURES 
 
 Figure Page 
 
 1. The Analog I/O Interface • 13 
 
 2. Time-Rate Changing Scheme 32 
 
 3. The Simple Reverberator 34 
 
 4. The All-Pass Reverberator 35 
 
 5. Logic Symbol Definitions 40 
 
 6. Clock and Filter Circuits 42 
 
 7. Control Circuits 44 
 
I. INTRODUCTION 
 
 The analog input/output (I/O) facility of the University 
 of Illinois Illiac II digital computer was designed primarily 
 for the processing of audio or other analog signals lying in 
 the frequency band to 20,000 Hz. The facility consists of 
 an audio tape recorder/reproducer, which is the source or 
 receiver of analog signals, and an analog I/O interface that 
 accomplishes both analog-to-digital (A/D) and digital-to- 
 analog (D/A) signal transformation. Control of the audio 
 tape machine and transfer of digitized analog signal infor- 
 mation to or from the Illiac II are two additional functions 
 of the analog interface, and the latter operation may be 
 activated only by command from a program in the Illiac II. 
 
 By using the Illiac II in conjunction with the analog 
 I/O facility it is possible to perform detailed Fourier 
 analysis of complex audio wave forms, such as those pro- 
 duced in speech or music, and to re-synthesize these wave 
 forms. Simpler processes such as time and amplitude trans- 
 formations of existing audio signal information or genera- 
 tion of artificial signals are also possible. 
 
 Systems similar to the Illiac II facility are in use 
 at several locations, notably Stanford University and Bell 
 Telephone Laboratories. The fields of research being in- 
 vestigated at the University of Illinois and these locations 
 generally fall into two categories: Namely, 1) Analysis and 
 synthesis of speech and musical instrument tones and 2) gen- 
 
eration of electronic music. 
 
 1.1. The Analog I/O Interface 
 
 The primary purpose of the analog I/O interface is to 
 perform transformations between analog and digital signals. 
 During the input operation, the interface produces digital 
 values (called samples) within uniformly spaced time inter- 
 vals (called sample periods). Each digital value represents 
 the amplitude of the incoming audio signal at the beginning 
 of the corresponding time interval. The Illiac II simultane- 
 ously reads eac:. sample into its memory and thereby obtains 
 a stair-step digital approximation in time of the actual 
 analog signal. Analog output is performed by an inverse 
 process in which the Illiac II periodically supplies the in- 
 terface w: '. digital samples (representing a stair-step 
 
 approximation to the actual signal) , whicn the interface 
 converts to analog voltage levels. The resulting stair-step 
 output vc-tages are filtered to produce the desired smooth 
 wave for:.. . 
 
 The transformations performed by the interface are exe- 
 cuted bv A/D and D/A converters. The D/A converter consists 
 of a flip-flop register with the output of each flip-flop 
 connected to a Kirchoff voltage adder. When a binary number 
 is stor-d into the register by the Illiac II, the voltage at 
 the out /at of the voltage adder becomes numerically propor- 
 tional _o the value of the binary number. 
 
 T,.w A/D converter is more complex since it uses a pro- 
 
cess of successive approximations to obtain the result. 
 While there are many different A/D conversion techniques^- 
 the most common method is to systematically alter the 
 input to an internal D/A converter until the output of the 
 D/A converter equals the value of the input voltage. The 
 binary number that produces this result is the required 
 digital value. 
 
 I. 1.1. Precision of Representation 
 
 The precision to which the stair-step digital approxi- 
 mation represents the actual analog signal is determined by 
 the resolution of the interface in both amplitude and time. 
 
 I. 1.1.1. Amplitude Resolution 
 
 Amplitude resolution is a function of the number of 
 binary digits (bits) used to represent the analog signal 
 amplitude at each sampling period. As the number of bits 
 used to represent a number increases, the fractional error 
 in its value caused by an uncertainty of +1/2 in the least 
 significant bit (lsb) decreases. Since a similar uncer- 
 tainty also exists in the analog signal amplitude due to 
 additive noise, in practice it is only necessary to use 
 enough bits in the digital representation so that the uncer- 
 tainty in the lsb is below the noise level of the analog 
 signal. To compute the "signal-to-noise (S/N) ratio" for a 
 
 -•■Stephenson, B.W., Analog-Digital Conversion Handbook , 
 Digital Equipment Corp., Maynard, Mass. 
 
digital sample value, consider a sample represented by n 
 
 bits plus sign. The maximum value is ±2 n -l and the "noise" 
 
 value is ±1/2. The S/N ratio for the sample is thus 
 
 S/N = 20 -log 2n " 1 
 y 10 ^72 
 
 « 20 -log 2 n+1 
 10 
 
 - 6«(n+l) decibels (1-1) 
 In the Illiac II system 12 bits (13 bits including the sign) 
 are used for conversion. This is equivalent to a S/N ratio 
 of 78Gb, which far exceeds the present 65db S/N ratio of 
 the tape recorder/reproducer and allows excellent amplitude 
 representation. In addition , the 13 bit samples are 
 optimally packed 4 per word inside the Illiac II memory 
 since the word length for this computer is 52 bits. 
 
 1.1.1.2. Time Resolution 
 
 Time resolution is a function of the length of the sam- 
 pling period or the sampling rate (sampling rate = 1/sampl- 
 ing period) of the conversion system used. If an analog 
 signal is presumed to consist of frequencies in the band of 
 to f Hz then the sampling theorem 2 requires that a sampling 
 rate of at least 2f be used in order to resolve all frequen- 
 cies within the band. When the sampling rate is 2f, fre- 
 quencies greater than f are also mapped into the range to 
 f by the sampling process and thus cause a distortion in the 
 
 2 
 
 Susskind, A.K. , Notes on Analog-Digital Conversion Tech- 
 niques , MIT Press, Cambridge, Mass. 
 
digital representation. In this mapping process, called 
 "frequency foldover" , the frequencies in the ranges nf 
 to (n+l)f (n=l,2...) are linearly mapped onto the range 
 to f if n is even and onto the range f to if n is odd. 
 
 The Illiac II system is capable of operating at a 
 sampling rate of 40,000 Hz which permits accurate repre- 
 sentations of audio signals in the range of to 20,000 Hz. 
 Sampling frequencies of 10,000 Hz, 20,000 Hz, and 30,000 
 Hz are also available for lower bandwidth signal processing. 
 
 1.1.1.3. Over-ranging 
 
 With a system which uses digital representations for 
 analog signal sample values it is necessary that the ampli- 
 tude and spectral frequencies of the signals to be processed 
 lie within certain specified limits. When these limits are 
 exceeded, over-ranging in both frequency and amplitude may 
 distort the signal. The results of such actions are 1) fre- 
 quency foldover when the bandwidth of the signal exceeds 1/2 
 the sampling frequency and 2) amplitude clipping of wave- 
 forms when the maximum amplitude limits are exceeded. In 
 the case of analog input, the first type of over-ranging 
 can be corrected by applying low pass filtration and the 
 second type by amplitude attenuation of the analog signal. 
 These operations restrict the signal so that it conforms to 
 the limits imposed by the finite sampling rate and the fi- 
 nite digital word length of the I/O interface system. In 
 the case of analog output it is up to the programmer to in- 
 
sure that the signal does not exceed the over-ranging 
 limits in either frequency or amplitude. 
 
 1.2. Digital Data Storage 
 
 Digital samples are transferred to or from the Illiac 
 II one at a time and at a rate determined by the sampling 
 frequency of the analog I/O interface. While the samples 
 could be actively stored and 'processed in core memory, this 
 is not usually feasible because of the limited capacity of 
 the Illiac II memory (8192 words or 32,768 samples) for any 
 of the sampling frequencies used. 
 
 As an alternative, the samples may be stored on one of 
 the three available secondary storage devices (namely, mag- 
 netic drum, disk, or tape) in "records" of about 1000 to 
 4000 samples. With such a scheme, overall signal process- 
 ing is accomplished in three steps: Namely, 1) analog input 
 onto the secondary storage device, 2) processing of the data 
 or creation of artificial data, and 3) analog output from 
 the secondary storage device. While the use of secondary 
 storage is more time consuming than a direct "in core" pro- 
 cessing approach, it provides for a much more flexible 
 system. 
 
 1.2.1 Selecting the Storage Device 
 
 The selection of a secondary storage device depends on 
 the type of processing to be done and is determined by 1) the 
 maximum sampling rate to be used and 2) the maximum number of 
 
samples to be transferred. We will assume that the maximum 
 
 time required for the storage device to "get to" a record 
 
 of samples (the access time) is t seconds and that the time 
 
 to transfer the record into core memory is t, seconds. If 
 
 b 
 
 the sampling rate is f samples/second and the record size is 
 n samples then the inequality 
 
 t + t. .< n/f (1-2) 
 
 a b 
 
 must be satisfied for the storage device to be usable. Also, 
 assuming that equation 1-2 is satisfied, the maximum storage 
 capacity of the device must be at least as great as that re- 
 quired by the processing application. 
 
 For the magnetic drum t = 16.7 ms (the time for one 
 
 a 
 
 revolution), tr= 2.08 ms , and n is fixed at 1024. It follows 
 that the maximum usable value of f is greater than 40,000 so 
 that the drum can be used at any of the available sampling 
 rates. On the other hand, the drum is limited by its stor- 
 age capacity of approximately 260,000 samples, which allows 
 only 6.5 seconds of audio signal storage at the 40,000 Hz 
 sampling rate. 
 
 The magnetic disk 4 , an IBM 1302 disk file, has a total 
 capacity of over 20 million samples, which would allow more 
 than 8.5 minutes of continuous audio signal storage at the 
 40,000 Kz sampling rate if this rate could be maintained. 
 
 3 
 
 Gillies, D.B. , Special Registers and Interrupts for the 
 
 Illiac II , University of Illinois, DCS, Urbana, Illinois. 
 
 4 
 Willard, il.E. , Programming Aspects ^f the Disk File Channel 
 
 University of Illinois, DCS, Ur:oana, Illinois. 
 
8 
 
 The access time, however, may range from 33.3 ms to 0.18 sec 
 with this device, depending on the location of the record, 
 while the record transfer time is approximately 25.6 ms. 
 Since n = 1024, the maximum value of f is less than 20,000 
 making the disk unusable at the higher data rates where its 
 total capacity is required. Therefore, for very large stor- 
 age requirements, magnetic tape must be used. 
 
 The Illiac II has available two magnetic tape channels-* 
 and has the capability for transferring records with lengths 
 equal to some multiple of 1024 samples. As is explained 
 below, both tape channels can be used instead of one in 
 order to reduce the effect of the record access time for one 
 unit. 
 
 Each tape drive (IBM 729 model VI) has a maximum ac- 
 cess time of t = 10 iris (the inter-record gap time) and a re- 
 a 
 
 cord transmission time of t,= n/40,000 seconds assuming use 
 
 of the 800 bits/inch Illiac II binary format. The inequality 
 
 stated by 1-2 thus reduces to: 
 
 f < 40,000 n 
 
 n+400 (1-3) 
 
 indicating that for n > 1200, a sample rate of 30,000 samples/ 
 second can be used, but that for f = 40,000, n must be infin- 
 ite. 
 
 Both tape channels can be used to achieve the 40,000 
 
 5 
 Pis-cerz^, M.J. , Programming Aspects of the Magnetic Tape 
 
 Interplay Channels , University of Illinois, DCS, Urbana, 
 
 Illinois. 
 
samples/second rate by overlapping the time for data trans- 
 mission on one channel with the record access time on the 
 other channel. With such a system, sample records which 
 are adjacent in time are recorded alternately on two differ- 
 ent tapes in such a way that if the records were numbered 
 1, 2, 3 ... in time, then all odd-numbered records would be 
 on one tape and all even-numbered records on the other. 
 The storage capacity of a single 2400 foot reel of 
 magnetic tape is approximately 8 million samples which 
 allows more than 4.5 minutes of continuous audio signal 
 storage at 30,000 samples/second with a single tape system 
 or over 6.7 minutes at 40,000 samples/second with a two 
 tape system. 
 
 1.2.2. Data Transfer Errors 
 
 Errors occurring in the transfer of information between 
 drum or tape and core memory fall into two categories: 
 Namely 1) parity errors and 2) wrong-length-record errors 
 (tape only) . Parity errors generally indicate an error in 
 one or more bits of information and can be ignored as 
 "noise" for most applications. Wrong-length-record errors, 
 however, indicate a loss of one or more words (4 samples) 
 of information during reading. This kind of error is gener- 
 ally due to an initial mispositioning of the tape and can be 
 corrected by subsequent backspacing and re-reading. During 
 analog I/O such operations cannot be performed in real time. 
 Therefore, the error (which often produces an audible "click") 
 
10 
 
 might not be ignorable, depending on the application. 
 
 For the two tape system, a wrong length record intro- 
 duces a far worse secondary effect. If the error was caused 
 by a digital tape dropout (loss of information) instead of 
 mispositioning, the tape channel may consider the dropout 
 to be the end of the record. In this case the remainder of 
 the record may be interpreted (by the tape channel) to be 
 another record, thereby destroying the sequencing between 
 the two tapes. Unless further information is provided in 
 each record, such as a sequence number, this error is suf- 
 ficient cause for termination of the analog output opera- 
 tion since the remainder of the analog signal would be hope- 
 lessly distorted. 
 
 1.2.3. 1? roc-ramming Analog I/O 
 
 Programs to perform continuous analog I/O with magnetic 
 drum or tape require the use of a multiple buffering scheme 
 so as to provide a continuous flow of samples between the 
 Illiac II and the analog interface while discrete records are 
 being transferred to or from the secondary storage device. 
 To indicate the. general procedure, consider a program using 
 a single tape as its secondary storage device with records 
 of 512 words (or 2048 samples). Two buffers, each 512 words 
 lone, ^re set aside in core memory. During an analog input 
 operation the program reads incoming samples from the analog 
 interface, packs them 4 per word, and stores each filled 
 word in buffer 1. When buffer 1 is full the program sends 
 
11 
 
 I/O commands to the tape channel (a direct-memory access 
 device) to cause the contents of buffer 1 to be written 
 onto tape. Once the commands are given, the program then 
 proceeds to fill buffer 2 (as it did buffer 1) while the 
 tape I/O channel independently writes buffer 1 onto tape. 
 After buffer 2 is filled, the program checks the I/O chan- 
 nel to make sure the previous transfer is complete and then 
 commands the channel to write buffer 2 onto tape. The pro- 
 gram repeats the process by filling buffer 1 again and so 
 forth, allowing the continuous stream of input samples to 
 be separated into discrete records. Analog output is per- 
 formed by the inverse process. 
 
 A two tape system uses a scheme similar to that for 
 a single tape with the exception that four buffers are re- 
 quired to maintain the desired data flow instead of two. 
 Therefore, core storage equivalent to four times a single 
 record length must be reserved for the analog I/O operations 
 
 It should be mentioned that the key to implementation 
 of a program for analog I/O to or from digital tape, is the 
 direct-memory-access capability of the tape channels. With- 
 out this capability the tape drives and the computer's cen- 
 tral processor could not work independently in order to 
 maintain a continuous flow of data. The same type of chan- 
 nels are also provided for the magnetic drum and disk units 
 allowing either to be used, if required, in place of a 
 single tape in the procedure described above. . 
 
12 
 
 II. A DESCRIPTION OF THE ILLIAC II ANALOG I/O SYSTEM 
 
 II. 1. Operation of the Analog I/O Interface 
 
 The basic structure of the analog I/O interface and 
 its interconnection with the Illiac II is shown in Figure 
 1. All I/O operations performed by the interface are con- 
 trolled with a program in the Illiac by means of a double 
 flip-flop register known as "special register 58" or SR58. 
 A second identical register ("special register 54" or 
 SR54) is used to transfer the digital sample data to and 
 from the interface. 
 
 Each double register is 13 bits in length and actually 
 consists of a 13 bit output "side", into which the pro- 
 gram can set or store information from memory, and a 13 bit 
 input "side", that the program can read into memory. The 
 interface, however, can store information into the input 
 side, and read information from the output side of each of 
 the two registers, allowing samples to be transferred 
 through SR54 and control information to be transferred 
 through SR5 8. 
 
 Proper sequencing of information transfers is provided 
 by four control signals that are associated with each of 
 the special registers. Two of these (called ASN and FULL) 
 are generated in the special register control section of 
 Illiac II and are sent to the interface. The other two 
 (called EMI and RFULL) are generated by the interface and 
 sent to thus special register control.- 
 
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14 
 
 The signals ASN and EMI are used to control the input 
 sides of the registers. The signal ASN occurs when a pro- 
 gram in the Illiac reads the input side of either register 
 and is used to tell the interface that new data may be 
 stored. The signal EMI causes the new data to be stored 
 and "interrupts"^ the Illiac. This latter action is used 
 by the program to determine when new data is available. 
 The signals FULL and RFULL perform similar control functions 
 for the output sides of the registers. The signal FULL 
 occurs when a program stores new data into the output side 
 of either register, and is used to tell the interface that 
 new data is available. The signal RFULL resets FULL and 
 tells the special register control section that new data 
 may be stored. When FULL occurs, further attempts by the 
 program to store new data into the special register will 
 cause the Illiac to stop the program until RFULL is sent. 
 In this manner the previous data cannot be destroyed until 
 used by the interface. 
 
 The interface itself consists of 1) the A/D and D/A 
 converters, 2) control logic to sequence the I/O operations, 
 3) a clock pulse generator to provide the proper sampling 
 rate, 4) filters to smooth the analog output, and 5) the 
 audio tape recorder/reproducer. Program control of the in- 
 terface is performed by setting bits in the output side of 
 
 6 Gillies, D.B., Special Registers and Interrupts for the 
 Illiac II, University of Illinois, DCS, Urbana, Illinois. 
 
15 
 
 SR5 8. The control functions allow the program to either 
 start or stop analog I/O, and to simultaneously select 
 one of four sampling rates and its associated analog out- 
 put filter. (The RFULL signal for SR58 is continuously 
 sent to the Illiac allowing the program to change the out- 
 put side of this register at any time) . 
 
 During analog I/O, the interface control logic checks 
 to make sure that the program is keeping up with the sampl- 
 ing rate selected (i.e. , that it is reading samples in or 
 sending them out fast enough) . If either the program lags 
 behind or the A/D converter does not finish conversion in 
 time, the input side of SR5 8 is set to indicate an error 
 condition. When the program checks the error condition 
 flag by reading SR58, the ASN that is sent back to the in- 
 terface control logic, resets the error condition and 
 causes SR58 to be cleared. 
 
 II. 1.1. Analog Input 
 
 Analog input is started by setting the bit in SR58 
 which produces the signal "Select Input". When "Select 
 Input" goes on, the control logic starts the audio tape 
 machine in the playback mode and begins A/D conversion and 
 error checking. The correct sampling rate is determined 
 by setting two bits in SR58 which produce the signal 
 "Select Rate" that in turn controls the clock frequency. 
 
 At -che beginning of each sample period, the clock 
 sends a pulse to the control logic, which in turn checks 
 
16 
 
 for errors (as previously described) and sends a "Start 
 Conversion" signal to the A/D converter. At the com- 
 pletion of conversion a "Conversion Done" signal is re- 
 turned by the A/D converter and is sent simultaneously 
 to the control logic for error checking and to the Illiac 
 as the EMI signal for SR54. The latter action indicates 
 that a new sample is ready. The ASN signal from SR54, 
 which indicates that the new sample has been read, goes 
 back to the control logic for error checking. 
 
 II. 1.2. Analog Output 
 
 Analog output is started by setting the bit in SR58 
 which produces the signal "Select Output". When "Select 
 Output" goes on, the control logic starts the audio tape 
 machine in the record mode and begins D/A conversion and 
 error checking. The sampling rate is selected in the same 
 manner as for analog input. 
 
 At the beginning of each sample period, the clock 
 pulse causes the control logic to send a "Start Conversion" 
 signal to the D/A converter which then reads and converts 
 the value stored in the output side of SR54. The same 
 signal is sent to the Illiac as RFULL for SR54. This 
 action allows the program to store a new value. When a 
 new value has been stored, the FULL signal that is returned 
 from SR54 is sent to the control logic for error checking. 
 
17 
 
 II. 1.3. Termination of Analog I/O 
 
 Analog I/O is terminated when the program resets the 
 output side of SR58 so that both "Select Input" and 
 "Select Output" are turned off and "Stop I/O" is turned on. 
 When both "Select Input" and "Select Output" are turned 
 off, transmission of the clock pulses through the control 
 logic is prevented, and all conversion and I/O operations 
 from the interface are halted. The "Stop I/O" signal is 
 required by the control logic in order to automatically 
 stop the audio tape machine after it has been started in 
 the record or playback mode by the previous analog I/O 
 operation. 
 
 Detailed information concerning the interface "hard- 
 ware" is given in Appendix A. 
 
 II. 2. Programming the Analog I/O Interface 
 
 The programming of analog I/O is performed by use of 
 the ASN and SSR instructions, which allow a program to read 
 data from the input side and store data into the output side 
 of a special register. Thus, the program can transmit sam- 
 ples via SR54 and control the interface and check for errors 
 via SR5 8. 
 
 The major problem that arises in programming is to 
 keep in step with the interface. During output it is only 
 
 7 If both "Select Input" and "Select Output" are turned on, 
 the interface will attempt to perform both input and out- 
 put but tile audio tape .machine will be set to record. 
 
18 
 
 necessary for the program to execute a store (SSR) in- 
 struction for SR54 before the end of each sample period, 
 thereby allowing the Illiac to guarantee synchronization 
 by holding up the program until the end of each period. 
 Since this cannot be done during analog input, a third 
 special register, SR14, is available in the Illiac to 
 tell the program when an EMI has been sent to certain of 
 the other special registers (including SR54 and SR58) . 
 
 By use of SR14, the program can tell when the ana- 
 log I/O interface has sent an EMI to SR54 indicating the 
 end of conversion and the availability of a new sample. 
 In this manner proper synchronization can be maintained 
 to prevent loss of samples. 
 
 II. 2.1. Using the Digitized Samples 
 
 Samples sent to and from the interface are 13 bit 
 binary numbers in 2's complement notation. The values 
 range from +4095 for the positive voltage maxima to -4095 
 for the negative voltage maxima with zero equaling zero 
 volts. 
 
 Due to the 13 bit quarter word structure of the 52 
 bit Illiac II words, the samples are conveniently packed 
 4 per word for compact storage. For computational purposes, 
 the samples may be easily converted to normalized floating 
 point and inversely. Single instructions perform the con- 
 versions automatically when the range is restricted to 
 absolute values of less than 1.0 in the floating point form. 
 
19 
 
 Detailed information concerning the programming of 
 the interface is given in Appendix B. 
 
 II. 3. The Analog I/O Programming System 
 
 The analog programming system was written to make 
 the Illiac II analog I/O facility available to those users 
 who are unfamiliar with machine language programming. The 
 system consists or a program that performs continuous ana- 
 log I/O using digital magnetic tape as the secondary stor- 
 age medium, and a set of subroutines that allow these tapes 
 to be read and written by user programs written in FORTRAN. 
 
 The first version of the analog programming system 
 used both tape channels and two tapes in order to allow 
 analog I/O at the- 40,000 Hz sampling rate. Use of the 
 system indicated that its major drawback was frequent occur- 
 rences of wrong-length-record errors, which necessitated 
 premature termination of analog output operations. As a 
 result, a second version was written using a single tape 
 and long records. This bypasses the need for program ter- 
 mination when a wrong length record is encountered. The 
 new system allows use of all available sampling rates ex- 
 cept for 40,000 Hz. 
 
 The original system, consisting of the analog I/O pro- 
 gram (called ADSYS) and the tape I/O subroutines for FORTRAN 
 (called ADPAK) , is available to users requiring the 40,000 
 Hz sampling rate. A complete description of the use of the 
 programs is given in reference 3 of the bibliography. The 
 
20 
 
 programs in the new system (called ADSYS2 and ADPAK2 , 
 respectively) are described below. 
 
 II. 3.1. ADSYS2 
 
 ADSYS2 is a machine language program to perform ana- 
 log I/O to and from a digital magnetic tape supplied by the 
 user. The user's tape consists of a set of sample files 
 each containing one or more records of digital samples in 
 a format that can be used by the ADPAK2 subroutines. The 
 sample records in each file constitute the digital repre- 
 sentation of a continuous analog signal beginning at the 
 start of a file and terminating at the start of the next 
 sequential file. In this manner, more than one continuous 
 analog signal may be stored on a tape so that the handling 
 of large numbers of signals is made convenient. (The orig- 
 inal version allowed only one continuous signal per pair 
 of reels). In addition to the sample records, each file 
 contains a file label record and each tape contains a tape 
 label record as a means of uniquely identifying the tape 
 and the files stored on it. 
 
 In actual operation analog I/O is not performed direct- 
 ly onto or from the user's tape because the records used are 
 too short to maintain a 30,000 Hz sampling rate (See Section 
 1.2). Instead an intermediate tape (called the conversion 
 tape) is used on which long records are stored. To perform 
 input the user specifies to ADSYS2 the sample rate and the 
 total time of input and then requests that the operation pro- 
 
21 
 
 ceed. When the i^put is finished, the digitized signal 
 is stored on the conversion tape as a single file of long 
 records. If the user wishes to save the information he 
 may then request ADSYS2 to copy the conversion tape into 
 a file on the user's file tape, thereby making it avail- 
 able for processing. Output is performed inversely by 
 first requesting a file to be copied from a file tape onto 
 the conversion tape as a single file of long records and 
 then requesting analog output. In either case, the copying 
 operations properly convert the record sizes so that no 
 samples are lost. 
 
 By use of the conversion tape it is possible to pro- 
 vide users with access to the 30,000 Hz sampling rate. 
 In addition, sample records stored on the conversion tape 
 are not destroyed (during a single loading of the program) 
 until over-written by a copy or input operation. Thus it 
 is possible to check the digitized analog input samples 
 by doing analog output and performing a visual or aural 
 check on the converted signal before transferring the 
 samples to the file tape. It is also possible to retry 
 faulty analog output operations without additional copying. 
 
 II. 3. 1.1. Using ADSYS2 
 
 All operations performed by ADSYS2 are determined by 
 a set of commands which are communicated to the program 
 via a teletypewriter console connected on-line to the Illiac 
 II. The iiix basic operations specified by command are 
 
22 
 
 a 
 
 1) labeling of a new file tape, 2) copying a file onto 
 the conversion tape, 3) copying the conversion tape onto 
 a file tape, 4) analog input, 5) analog output, and 6) 
 internal generation of sine and sawtooth tones for analog 
 output. Each command is input to the program by typing 
 the name of the operation to be performed followed by a 
 string of job parameters. The job parameters are used to 
 tell ADSYS2 such information as the sampling rate, the 
 time limit for I/O, the file to be copied into or from, 
 which tape drive the file tape is on, and so forth. 
 
 When a command is given, the system verifies all the 
 input parameters and, if tape copying or labeling was 
 specified, generates or checks the tape and file labels 
 on the user's file tape and then performs the operation. 
 For analog I/O or tone generation a message is then sent 
 to the on-line teletypewriter indicating the system is 
 ready to perform the requested operation. The operation, 
 however, does not proceed until a switch is set on the 
 Illiac II console. This gives the operator time to mount 
 any required audio tape. 
 
 Once started, an operation continues until it is com- 
 pleted, (in the case of copying and tape initialization) 
 or it continues until an end condition is detected (in the 
 case of analog I/O) . End conditions may occur if the con- 
 sole switch is reset, the specified time limit is exceeded, 
 or for other reasons. Upon termination, ADSYS2 sends a 
 
23 
 
 final message to the on-line teletypewriter indicating 
 that the operation has been completed. It is then pre- 
 pared to accept the next command. All tape errors oc- 
 curring during analog I/O are ignored; however, tape 
 errors detected on the file tape during copying opera- 
 tions cause the record to be re-read or re-written 
 several times before being ignored. Analog interface 
 errors are counted and output with the final message but 
 are otherwise ignored. Detailed information regarding 
 the tape record formats and the command language is given 
 in Appendix C. 
 
 I^AA, 
 
 ADPAK2 is a collection of machine language subrou- 
 tines that ailov; programs written in FORTRAN (or machine 
 language) to read and write the file tapes used by ADSYS2. 
 The subroutines are divided into two groups with four sub- 
 routines in each group. One group is used to input an 
 existing file of samples while the other is used to create 
 a new file of samples. In addition, a ninth subroutine 
 provides the means for creating a tape label on a previously 
 unused file tape. 
 
 ^'r.a subroutines in the input/output groups are used 
 to "activate" and "deactivate" files on the file tape, to 
 transfer sample records between core memory and tape, and 
 to skip over sample records or generate sample records con- 
 taining all zeros. A file is activaced by first checking 
 
24 
 
 the tape label and then searching the tape and checking 
 each file label until the requested file is found. If 
 the requested file is not found and the file is being 
 activated for input, the program terminates. If, however, 
 the file is being activated for output, a new file is 
 created at the end of the last file on the tape and the 
 program continues. Once activated, the file remains ac- 
 tive until it is deactivated. During this period, sample 
 records may be read or written and record skipping or 
 zero record generation may be performed. 
 
 A file is deactivated by writing the proper file ter- 
 mination marker (in the case of an output file only) 
 and/or rewinding the tape on which the file is located. 
 Deactivation occurs automatically when the end of an active 
 file is reached during the transfer of sample records or 
 can be requested by calling an appropriate subroutine. 
 Attempts to read or write sample records when there is no 
 active input or output file, respectively, are ignored. 
 
 The samples transferred between core memory and tape 
 are written or read in records of 1024 samples each. 
 ADPAX2 performs a conversion so that all input samples are 
 stored as normalized floating point numbers with absolute 
 values less than 1.0. On output, the inverse conversion 
 is performed and samples whose absolute values are equal 
 or greater than 1.0 will cause accumulator overflow. 
 
 All tape errors cause the assc elated read or write 
 
25 
 
 operation to be retried a maximum of 10 times. If the 
 error persists on the 10th retry, it is ignored, and a 
 flag is returned to the calling program indicating the 
 error. Detailed information regarding the required call- 
 ing sequences is given in Appendix D. 
 
26 
 
 III. TWO EXAMPLES OF USAGE OF THE ILLIAC II ANALOG I/O 
 FACILITY 
 
 111.1. Current Status 
 
 The analog input/output system on the Illiac II is 
 currently being used by the departments of computer science, 
 music, and electrical engineering. This work includes 
 Fourier synthesis of musical instrument tones and various 
 experiments in music generation and processing. In the 
 latter category are the processes of time-rate changing and 
 synthetic reverberation, which will be discussed in detail 
 below. Future plans include research in speech analysis 
 and digital processing of analog data from experimental 
 apparatus. 
 
 111. 2. Time-Rate Changing 
 
 Time-rate changing is a process in which the duration 
 of a given audio signal is compressed or expanded in time 
 without changing the audible frequencies. In a musical 
 context this means that the tempo of the music is changed 
 while the pitches remain unaltered. This process differs 
 from the more common time-change process accomplished by 
 playing back a recorded signal at a rate different from 
 that at which the signal was recorded. In this case the 
 audible frequencies, as well as the tempo, vary in direct 
 proportion to the playback rate. 
 
 Time-rate changing can be performed by a special ana- 
 log apparatus using a variable speed capstan drive and a 
 
27 
 
 cylindrical revolving head with four gaps equally spaced 
 about its circumference. In operation the capstan and 
 tape head speeds are adjusted to maintain the same gap-to- 
 tape speed as was used to record the sound. Since the 
 tape covers slightly less than one-fourth of the revolving 
 head's circumference only one gap is in contact with the 
 tape at any time. Thus, since during playback the tape is 
 actually moving faster or slower with respect to the axis 
 of the head than it was when recorded, a small segment of 
 the tape is either deleted or doubly reproduced as one 
 head leaves and another comes in contact with the tape 
 surface. Those segments which are reproduced form a 
 piece-wise continuous signal that is shorter or longer in 
 duration than the original, but, due to the proper gap-to- 
 tape speed, the audible frequencies are the same as those 
 of the original. The distortion which results from such 
 a process depends on 1) the rate at which the segments are 
 deleted or doubled (called the "segmentation rate"), 2) the 
 degree of continuity between adjacent reproduced segments, 
 and 3) the percentage by which the durations are changed 
 (called the "degree of rate-changing"). 
 
 The segmentation process is essentially equivalent to 
 a time modulation. As a result minimum distortion in the 
 signal will occur when the segmentation rate is as far as 
 possible below the lowest spectral frequency component of 
 the signal. However, as this rate is decreased, the individ- 
 
28 
 
 ual reproduced segments can be audibly distinguished as a 
 "choppy-like" sound pattern. Therefore, it is necessary 
 to select a segment length shorter than can be recognized 
 by ear but longer than the period of the lowest frequency 
 to be processed. For normal musical material, segmenta- 
 tion rates of 20 to 30 segments per second seem to provide 
 the best compromise of these factors. (This may depend on 
 the kind of music being processed) . 
 
 The degree of rate-changing is in a sense the percent- 
 age by which the sound source is modulated, and the dis- 
 tortion introduced will be a function of the degree of 
 rate-changing. The audible effects of this distortion 
 range from near inaudiblity at small percentages (less than 
 5%) to a strong "warbling" of the sound at the segmentation 
 rate. This latter condition results from imperfect match- 
 ing of the amplitude values of the original signal at the 
 boundaries between reproduced segments. If "perfect" 
 boundary matching could be established, the rate changing 
 process would be greatly improved. However, this would 
 not only require matching the amplitudes but all of the de- 
 rivatives of the signal at the boundary points. Schemes 
 for matching the first few derivatives are described in the 
 following section. It must be noted, however, that there 
 is no possible way of achieving perfect rate-changing with- 
 out considerable a priori knowledge of the signal, and even 
 with such knowledge' the algorithm for "optimal" rate chang- 
 
29 
 
 ing may not be unique. 
 
 III. 2.1. Computer Simulation of Time-Rate Changing 
 
 The time-rate changing experiment was designed to 
 examine the aural effect of satisfying various types of 
 boundary conditions between segments produced by the pro- 
 cess described in III. 2. To perform such a task with an 
 analog system would have required a great deal of experi- 
 mentation with various mechanical setups and head config- 
 urations. On the other hand, a digital simulation of the 
 process allowed boundary conditions to be modified by 
 simple program changes. 
 
 Simulating the analog rate changer was one of the 
 simplest tasks to perform with the Illiac II analog- 
 digital facility. In operation, musical selections were 
 digitized and stored on digital tape using ADSYS. A 
 40KHz sampling rate was selected for maximum fidelity. 
 Then, using ADPAK, the rate changing program would input 
 into memory arrays of 16 samples each, one at a time. 
 This resulted in a segmentation rate of 25 segments per 
 second. The specified percentage of samples was then de- 
 leted (for time compression) or doubled and joined (for 
 time expansion) onto the end of a segment according to the 
 appropriate boundary matching algorithm. The resulting 
 modified segments were written by ADPAK onto the output 
 tape which was then converted by ADSYS into the rate- 
 changed audio signal. 
 
30 
 
 Two basic schemes of boundary matching were investi- 
 gated. With the first scheme the program was designed to 
 match the signs of the first derivatives of the signal at 
 zero axis crossings nearest the boundaries. In this case 
 the program examined samples beyond the end of the rate- 
 changed segment and beyond the beginning of the next 
 segment until the required boundary match was obtained. 
 As a result, the actual segmentation rate varied slightly 
 from segment to segment depending on the signal. This 
 caused a time- jitter distortion in addition to the distor- 
 tion due to segmentation, which is reduced by this process. 
 
 With the second scheme the end of each segment was 
 "blended" with the beginning of the next according to some 
 distribution function. The actual algorithm for this type 
 of time-rate changing is precisely stated as follows: 
 
 For time compression of a segment composed of samples 
 S., for i = 1 to N, with n samples to be deleted, the re- 
 sulting samples S', for i = 1 to N-n, are given by 
 S. [i = 1 to N-2n] 
 
 S. = \ P, *S. + (1-P, )*S. [i = N-2n+l to N-n; (III-l) 
 k l k l+n 
 
 k = i-(N-2n) ] 
 
 where P is a distribution function with values in the range 
 to 1 for k = 1 to n. For time expansion, where n samples 
 are to be added to each segment, the resulting samples S!, 
 where i = 1 to N+n, are given by 
 
s: = 
 
 31 
 
 t 
 
 S. [i = 1 to N-n] 
 
 i 
 
 P -S. + (1-P )-S. [i = N-n+1 to N; 
 k i k i-n (III-2) 
 
 k = i-(N-n)] 
 
 S. [i = N+l to N+n] 
 
 i-n 
 
 The process is shown schematically in Figure 2. 
 
 The distribution function, P, can vary from no blend- 
 ing (P = 1 or for all k) to more complex functions that 
 match the amplitudes and derivatives of the signal at the 
 boundaries of the blending region. As an example, the 
 
 function 
 
 P, = l-(k-l)/n (k = 1 to n) (III-3) 
 
 K. 
 
 will match boundary amplitudes properly while the function 
 
 P, = [1+C0SU- (k-l)/n)]/2 (k = 1 to n) (III-4) 
 
 k 
 
 will match both amplitudes and first derivatives properly. 
 In general, if the ith derivative of P is zero at k = 1 and 
 k = n for i = 1 to J, then the first J derivatives of the 
 signal will be matched at the boundaries of the blending 
 region. As more derivatives are matched, the boundary dis- 
 continuities are decreased but, at the same time, the deri- 
 vatives of P in the middle of the blending region become 
 increasingly larger. Since this factor also adds to the 
 overall distortion, it is necessary to compromise and select 
 a P that produces the best overall blending of the signal 
 segments. 
 
 III. 3. Synthetic Reverberation 
 
 Reverberation is a term applied to the collection of 
 
TIME COMPRESSION 
 
 32 
 
 B 
 
 /I / 
 
 / 
 / 
 
 1 
 
 / 1 
 
 / 
 
 A' 
 
 D' 
 
 ORIGINAL SEGMENT 
 (N Samples) 
 
 COMPRESSED SEGMENT 
 (N-n Samples) 
 
 TIME EXPANSION 
 
 B 
 
 l\ 
 
 l\ 
 
 / + \ 1 * + ^ 
 
 1 
 
 \ \ 
 
 \ 
 
 \ 
 
 1 
 
 \ 
 
 \ 
 
 \ 
 
 
 B* 
 
 E» 
 
 C 
 
 ORIGINAL SEGMENT 
 (N Samples) 
 \ 
 
 \ 
 
 \ 
 
 EXPANDED 
 
 SEGMENT 
 
 (N+n Samples) 
 
 A = 
 B = 
 C = 
 A' 
 B* 
 C 
 D' 
 E' 
 
 St tO S >T ~ 
 
 1 N-2n 
 
 S. T ~ , , to S X1 
 N-2n+l N-n 
 
 S XT .. to S x7 
 
 N-n+1 N 
 
 - A - S' to S' ^ 
 
 1 N-2n 
 
 = B = S* ~ .. to S' 
 
 N-2n+l N-n 
 
 - C " S m t0 S N+n 
 = P-B + (l-P)-C = S'. 2n+1 to S". n 
 
 = P-C + (l-P)-B = S-. n+1 to S^ 
 
 Figure 2. Time-Rate Changing Scheme 
 
33 
 
 echoes which are added to an audio signal by sound re- 
 flections in an acoustical environment. By artificial 
 means it is possible to simulate or supplement the rever- 
 beration produced by a concert hall. Several means of 
 producing synthetic reverberation by electro-mechanical 
 analog systems are currently available, but these are 
 generally deficient in one or more aspects. In an attempt 
 to circumvent these deficiencies, a detailed study of re- 
 verberation was carried out by M. R. Schroeder at Bell 
 Telephone Laboratories. 
 
 Schroeder' s analysis determined that the two main 
 problems which characterize existing reverberation equip- 
 ment are 1) non-uniform frequency response, and 2) in- 
 sufficiently large random echo density. One cause of non- 
 uniform frequency response in reverberators results from 
 the use of the simple ideal reverberator circuit shown 
 in Figure 3a. The response of this configuration is 
 given in Figure 3b. While an increase in pseudo-random 
 echo density is achieved by a series connection of such 
 reverberators (set for different values of gain, g, and 
 delay, t) , the frequency response of the final output 
 signal is still seriously distorted. 
 
 As a result Schroeder developed an all-pass rever- 
 berator (Figure 4a) . This unit has a uniform gain of 1 
 for all frequencies and allows one to cascade as many 
 units as necessary to provide the required echo density 
 
34 
 
 (a) Basic Circuit 
 
 1/U-g) 
 
 ResDonse 
 
 i/U+g) 
 
 (b) Frequency Response 
 
 Figure 3. The Simple Reverberator 
 
35 
 
 (a) Basic Circuit 
 
 
 
 
 - 
 
 S. 
 
 l 
 
 TIMES 
 
 -g 
 
 -g 
 
 •S. 
 
 l 
 
 
 
 
 
 
 
 .. . ^ 
 
 T. 
 lj-n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 T. 
 l 
 > 
 
 STORE 
 
 n 
 
 SAMPLES 
 
 TIMES 
 1-g 
 
 
 Y 
 
 
 fl O ( 
 
 \ Ik 
 
 ADD 
 
 t-. 
 
 ADD 
 
 •s r« 1 
 
 i 
 
 
 ■+: 
 
 * f 
 
 p 
 
 *~i 
 
 
 
 A 
 
 
 
 
 
 
 
 
 
 
 5. 
 
 
 
 
 TIMES 
 
 g 
 
 d-g" 
 
 ■ l-r 
 
 I 
 
 
 g- 
 
 T. 
 
 1 
 
 -n 
 
 T. 
 
 1 
 
 -n 
 
 
 (b) Digital Simulation 
 
 Figure 4. The All-Pass Reverberator 
 
36 
 
 without altering the frequency response. Extensive ex- 
 perimentation by Schroeder indicated that the series 
 connection of five all-pass reverberators with feedback 
 gains of +.7 and selected delays between 5 and 100 msec 
 will produce a reverberation effect that is comparable 
 with' that of a conventional concert hall. 
 
 III. 3.1. Computer Simulation of Reverberation 
 
 Using the Illiac II analog-digital system, it was 
 possible to artificially reverberate .musical passages by 
 simulation of Schroeder 1 s all-pass reverberator. The 
 overall logical scheme was similar to that used for the 
 time-rate change experiment. Only the actual computa- 
 tional process was different. Simulation of the all-pass 
 reverberator is performed by use of a table, treated 
 circularly, which represents the delay element t. If the 
 maximum delay is to be m samples then the delay table 
 must be m locations long. As each sample S. is input to 
 the reverberator, the corresponding output sample S! is 
 produced by the following operation: 
 
 S. = (l-g 2 )-T. - g-S. (III-5) 
 
 i 3 l-n 3 l 
 
 where T. is an entry in the delay table corresponding to 
 the signal input -co the delay element (see Figure 4b) at 
 time t seconds, or n samples, ago (n < m) . For each new 
 input sample, the corresponding entry in the delay table 
 T. is reset by the operation: 
 
37 
 
 T. = g.T. + S . 
 1 x - n x (III-6) 
 
 This provides the feedback around the delay element x, as 
 
 indicated in the figure. Note that the index for T is 
 
 interpreted modulo m, the table length, to be compatible 
 
 with the circular table interpretation. The simulation of 
 
 a cascaded series of such reverberators is achieved by using 
 
 the output of one pass of the simulator as input to the next 
 
 sequential pass and so forth. 
 
38 
 
 APPENDIX A. THE ANALOG I/O INTERFACE: EQUIPMENT, SIGNAL, 
 AND LOGIC DESCRIPTIONS 
 
 The reader should be familiar with Section II. 1 of 
 this thesis before attempting to read the following infor- 
 mation. 
 
 The A/D converter is an 8 bit bipolar unit manufac- 
 tured by ADCGM (Model 2 8C) . The input range maxima are 
 + 2.5 volts corresponding to sample values of +4064 and 
 -4095 read through SR54. A change in the least signifi- 
 cant bit is equivalent to a voltage change of + .01954 
 
 o 
 
 ^volts corresponding to a digital value change of + 32. 
 The maximum conversion rate is 100,000 samples per second. 
 
 The D/A converter is a 13 bit bipolar unit manufac- 
 tured by Texas Instruments (Model 854) . The output range 
 maxima are + 10 volts corresponding to sample values of 
 +4095 and -4095 stored in SR54. Changing the least signifi- 
 cant bit produces a voltage change of + .00244 volts. The 
 maximum conversion rate is 250,000 samples per second. 
 
 The -cape recorder/reproducer is manufactured by Scully 
 (Model 2 30). This is a half track, two channel unit that 
 accepts 1/4" audio tape at speeds of 7-1/2 and 15 inches per 
 second. ^he signal to noise ratio using Scotch 201 magnetic 
 tape is better than 60 db. The frequency response is flat 
 
 o 
 
 "This devi^fi is to be replaced by a 13 bit A/D. converter in 
 the near future. 
 
39 
 
 within + 2db from 35Hz to I8KH2 at 15 inches per second. 
 Only the left tape channel (closest to the deck surface) 
 is presently used for analog I/O. 
 
 A. 2. Audio Signal Conventions 
 
 The tape recorder/reproducer has been calibrated for 
 Scotch 201 recording tape. The record and playback level 
 controls are correspondingly marked so that when set appro- 
 priately the following conventions apply: 
 
 1) A maximum amplitude lKHz sine tone output 
 from the Illiac II (+ 4095) will produce 
 a db record level on the tape. 
 
 2) A lKHz sine tone recorded at db on the 
 tape will be input to the Illiac as a 50% 
 maximum value sine tone. 
 
 A. 3. Digital Signal Conventions 
 
 The digital signals within the analog I/O interface 
 and those sent to and from the. Illiac are equal to one of 
 two voltage levels at any particular time: volts stands 
 for logical 1 and -5 volts for logical 0. In certain por- 
 tions of the circuitry the level signals are converted into 
 short duration pulses for triggering and gating purposes. 
 
 A. 4. The Analog I/O Interface Circuitry 
 
 The complete logical diagrams of the clock, filter, 
 and control sections of the analog I/O interface are 
 shown in Figures 6 and 7. Definitions of the logic symbols 
 
40 
 
 Pulse Signal 
 (logical 1 for 500 nsec after being 
 logical for > 700 nsec) 
 
 ^ Level Signal 
 
 (remains logical 1 or for > 700 nsec) 
 
 A 
 3 
 
 AND Gate 
 (C = 1 when A and B both = 1) 
 
 B 
 
 
 
 > C 
 
 OR Gate 
 (C = 1 when either A or B or both = 1) 
 
 ^S 1 
 
 c 
 
 D 
 
 B 
 C 
 
 Set/Reset Flip-Flop 
 
 (C = 1, D = after A ■ 1} C ■ 0, D ■ 1 
 
 after B = 1; output changes are 
 
 delayed by 700 nsec) 
 
 Complementing Flip-Flop 
 
 (B and C exchange values 700 nsec 
 
 after A changes from to 1) 
 
 
 
 RD 
 
 NO 
 
 NC 
 
 
 oB 
 
 Relay Driver and Relay 
 
 (C and D are connected when A = 0; 
 
 C and B are connected when A = 1) 
 
 A 
 
 H ?G 
 
 -> B 
 
 Pulse Generator 
 (B occurs when A changes from to 1) 
 
 I C 
 
 Crystal Clock 
 (A is a square wave at the clock rate) 
 
 Figure 5. Logic Symbol Definitions 
 
41 
 
 used are given in Figure 5. The reader should be familiar 
 with the logic conventions before reading further. 
 
 A. 4.1. The Clock and Filter Circuits 
 
 The clock consists of a 30KH'z and a 40KHz crystal os- 
 cillator providing a square wave output. The signal from 
 the 40KKz oscillator is fed to a two stage counter which 
 produces outputs of 20KHz and lOKHz. The four signals are 
 then sent to a two stage relay tree that selects one of 
 the four as the desired clock frequency. Selection is 
 determined by the state of bits 2 and 3 (weight 1024 and 
 512) in the output side of SR58. A one stored in either 
 bit will cause the associated relay driver to turn on. 
 The square wave output of the relay tree is then sent 
 through a pulse generator which produces 50 nanosecond 
 pulses for use by the interface. 
 
 The filter "circuit consists of two low pass R-C net- 
 works used with the 40KHz and 30KHz clock frequencies and 
 two low pass L-C filters used with the 20KHz and lOKHz 
 clock frequencies (manufactured by TT Electronics, Inc.). 
 The frequency response characteristics of the R-C networks 
 roll off with a -6 db/octave slope above 20KHz and 15KHz 
 respectively. The L-C filters are characterized by -3 db 
 cutoff frequencies of 8.5 KHz and 4KHz with 60 db attenu- 
 ation frequencies of 17KHz and 9KHz, respectively. The 
 output of the D/A converter is fed simultaneously through 
 
10 KHz 
 
 42 
 
 ■0\ 
 
 RD 
 
 NO 
 NC 
 
 2 KHz 
 
 30 KHz 
 C 
 
 40 KHz 
 
 D/A 
 Converter 
 
 Output 
 
 AV — 
 
 •4 KHz 
 FILTER 
 
 Bit 2 
 
 ~ 
 
 £.5 KHz 
 FILTER 
 
 SR58 
 Output 
 
 Bit 3 
 
 15 KHz 
 FILTER 
 
 RD 
 
 NO 
 
 NC 
 
 RD 
 
 NO 
 
 NC 
 
 RD 
 
 NO 
 
 PG 
 
 SR5 8 
 Output 
 
 <j o 
 
 20 KHz 
 
 FILTER 
 
 RD 
 
 RD 
 
 NO 
 
 Clock 
 > 
 
 Pulses 
 
 NC 
 
 NO 
 
 Tape 
 
 if Recorder 
 -y^fi— — o 
 
 Input 
 
 NC 
 
 Figure 6. Clock and Filter Circuits 
 
43 
 
 individual coupling resistors to the inputs of all four 
 filters. The filter outputs enter a relay tree, identical 
 to that used to select the clock frequency, and are ter- 
 minated by an attenuater which supplies the signal to the 
 tape recorder. Since the output impedance of the D/A 
 converter is very low (=^0.1 ohms) the series resistors 
 at the inputs to the filters provide both the proper 
 source resistances for the filters and a decoupling amongst 
 the four of them. 
 
 The clock and filter circuits are connected and oper- 
 ating at all times independent of what analog I/O is being 
 performed. The actual connections within the circuits, 
 corresponding to one of the four clock frequencies, are 
 dependent solely on the setting of bits 2 and 3 of SR58. 
 
 A. 4. 2. The Control Circuits 
 
 The action performed by the control circuitry is deter- 
 mined completely by bits 4, 5 and 7 (weights 256, 128 and 
 32) of the output side of SR58. In the quiescent state 
 (all bits in SR58 equal to zero) no action is performed by 
 the control circuits and the tape recorder is under complete 
 manual control. 
 
 For analog input bit 5 of SR58 is set to a one. This 
 gates the clock pulses into the A/D section of the circuitry 
 and closes the START relay so as to hold the tape recorder 
 in the playback mode. At the beginning of each sample cycle 
 the A/D clock pulse clears the "End o r Conversion" (CNDN) 
 
44 
 
 A/D 
 
 Conversion 
 
 Done 
 ASN 
 
 
 
 PG 
 
 EMI 
 
 
 
 SR54 
 
 
 
 ASN 6 6 
 
 
 
 
 
 
 
 PG 
 
 
 k 
 
 S 1 
 R 
 
 
 . N 
 
 A 
 
 
 n 
 
 
 
 
 SR54 
 Bit 5 
 
 
 ^4> 
 
 O 
 
 
 
 w 
 
 EMI 
 
 
 < 
 
 
 
 SR58 
 
 
 V 
 
 
 SR53 
 C- 
 
 output 
 
 A 
 
 
 
 
 
 
 
 
 A/D Start 
 
 
 
 
 
 
 i 
 
 ... y. 
 
 Conversion 
 
 Clock 
 
 < 
 
 :ndn 
 
 
 
 
 
 
 Pulses 
 
 
 
 -* 
 
 S 1 
 R 
 
 
 K 
 
 A 
 
 
 RFULL 
 
 
 v. 
 
 
 
 • 
 
 SR54 
 
 Clock 
 Pulses 
 
 
 
 r> 
 
 A 
 
 
 
 
 
 
 
 • 
 Bit 4 
 
 
 D/A Start 
 
 
 SSR6 6 
 
 
 
 Conversion 
 
 SR58 
 Output 
 
 , 
 
 
 
 
 
 
 
 
 
 
 PG 
 
 . 
 
 Si 
 
 R 
 
 
 
 
 
 
 ^L 
 SR54 
 
 
 * 
 
 — o 
 
 A 
 
 
 : 
 
 
 
 
 
 
 
 
 ERR 
 
 
 
 
 
 
 -- 
 
 S 1 
 
 R 
 
 Bit 12 
 
 ASN 
 ^ 
 
 SR58 
 
 
 
 
 
 
 w 
 
 SR5 8 
 
 PG 
 
 Pb 
 
 .. 
 
 Input 
 
 ' 
 
 
 
 
 
 
 
 START 
 
 
 
 Bit 5 SR58 
 
 
 
 
 RD 
 
 
 Output 
 
 
 ■o 
 
 NO 
 
 
 
 
 
 Bit 4 SR53 
 
 
 ' 
 
 
 
 Tape Recorder 
 
 Output 
 
 
 
 
 
 RECORD Control Input 
 
 
 
 RD 
 
 
 
 
 o 
 
 NO 
 
 
 
 Taoe Recorder 
 
 
 
 STOP Control Input 
 
 Bit 7 SR53 
 
 o 
 
 RD 
 
 
 Output 
 
 NC 
 
 
 
 
 
 
 
 
 
 
 Figure 7. Control Circuits 
 
45 
 
 flip-flop and signals the A/D converter to begin conver- 
 sion. If (CNDN) was not set to 1 during the previous 
 sample cycle the "Error" (ERR) flip-flop will be set to 
 1 at this time. When "Conversion Done" occurs, CNDN is 
 set to 1, and a pulse is sent to the EMI inputs of SR54 
 and SR5 8. This causes the outputs of the A/D converter 
 and the flip-flop ERR to be gated into the input registers. 
 After the contents of SR54 are read by a program in the 
 Illiac II, the ASN signal for SR54 is sent to the inter- 
 face which, in turn, sets to 1 the "ASN Done" (ASN6 6) 
 flip-flop. If this flip-flop is not set by the time the 
 next "Conversion Done" pulse occurs ERR will be set to 1. 
 The ASN6 6 flip-flop is reset by the "Conversion Done" 
 pulse, while ERR is reset by the ASN signal from SR58. 
 
 For analog output bit 4 of SR58 is set to 1. This 
 gates the clock pulses into the D/A section of the control 
 circuitry and closes the START and RECORD relays so as to 
 hold the tape recorder in the record mode. At the beginning 
 of each sample cycle the D/A clock pulse is sent to the 
 D/A converter causing it to gate the contents of the output 
 side of SR54 into its own internal register thus producing 
 a new analog value. The D/A clock pulse is also sent to 
 the RFULL input of SR54 and to the EMI input of SR58, en- 
 abling the program in the Illiac II to store a new sample 
 in SR54, and causing the flip-flop ERR to be gated into 
 the input ^ j de of SR58, respectively. When the output 
 
46 
 
 side of SR54 has been reset by the program, the signal 
 FULL is sent to the interface which in turn sets to 1 the 
 "SSR Done" (SSR66) flip-flop. If SSR66 is not set to 1 
 at the beginning of each D/A sample cycle, ERR is set to 
 
 1. SSR56 is reset by the D/A clock pulse and ERR is re- 
 
 9 
 set by the ASN signal from SR58. 
 
 Analog input or output is terminated by resetting 
 
 bits 4 and 5 of SR58 to zero. When this is done, the tape 
 
 recorder is returned to manual control but is left running 
 
 in the state previously selected (playback or record) . 
 
 To stop the recorder, bit 7 of SR58 is set to 1 for about 
 
 C.2 seconds, and then reset to thereby momentarily 
 
 activating the STOP relay. If bit 7 remains set to 1, the 
 
 recorder is held in the stop position by the STOP relay 
 
 and cannot be manually controlled. 
 
 ^Note that while ERR is reset when SR58 is read, the in- 
 put side of SR58 is reset only when ERR is gated into it 
 (i.e., at the next occurrence of "Conversion Done" during 
 input or r.he D/A clock pulse during output) . 
 
47 
 
 APPENDIX B. THE ANALOG I/O INTERFACE: MACHINE LANGUAGE 
 PROGRAM CONTROL 
 
 The reader should be familiar with Section II. 2 of 
 
 this thesis and the Illiac II symbolic machine language, 
 
 NICAP-*- , before attempting to read the following informa- 
 tion. 
 
 B.l. Analog Input 
 
 Input conversion of an analog signal recorded on audio 
 tape is initiated by the following sequence of instructions: 
 
 (1) ATN 128+F 
 
 (2) SSR 58 
 
 (3) (Delay loop of 1 second) 
 
 (1) and (2) set the output side of SR58 to the value 
 128+F where F is a previously defined constant. The 128 
 (bit 5) selects analog input and starts the tape recorder 
 in the playback mode. The bits defined by F select one of 
 the four sampling rates. The delay loop (3) allows the 
 tape recorder to stabilize but is not absolutely required. 
 The allowed values for F are: 
 
 for 40,000 samples per second 
 1024 " 30,000 
 512 " 20,000 
 1536 " 10,000 
 At the end of each sample conversion, bit 2 (weight 1024) 
 
 10 Gear, C.W. , Illiac II Manual , University of Illinois, DCS, 
 Urbana, Illinois. 
 
48 
 
 of SR14 is set to 1. This indicates that the sample is 
 ready to be read. If the corresponding mask bit in SR22 
 is set and "interrupts are enabled", the program will be 
 interrupted at this point. H Otherwise, this bit must 
 be tested by a program loop. Experimentation has shown 
 the shortest test-and-read loop to be the following: 
 
 FLD 
 
 (1) ASN 14 
 
 (2) CAM N / -1025 
 
 (3) CJF N 
 
 (4) ASN 54 
 
 ( 5 ) CAM M 
 
 (6) CNN 
 
 (7) SSR 14 
 
 (i) and (2) s'core in modifier N the contents of SR14 minus 
 1025. If bit 2 is not on, modifier N will contain -1025 
 and (3) will transfer control back to (1). However, when 
 bit 2 is set, modifier N will contain -1 allowing control 
 to pass onto (4) . (4) and (5) store into modifier M the 
 sample value while (6) and (7) reset SR14 to zero. 
 Analog input is terminated by the sequence 
 
 (1) ATN 32 
 
 (2) SSR 58 
 
 (3) (Delay loop = . 2 sec) 
 
 11 Gillies, D.3. , Special Registers and Interrupts for the 
 Illiac 17 , University of Illinois, DCS, Urbana, Illinois 
 
49 
 
 (4) SSR 58 
 
 (1) and (2) reset the output side of SR58 to 32 
 (bit 7=1) which terminates analog I/O and stops the 
 tape recorder. (3) is required to allow time for the 
 relays in the tape recorder to function while (4) resets 
 the output side of SR5 8 to zero allowing manual control 
 of the recorder. 
 
 B.2. Analog Output 
 
 Analog output to the audio tape recorder is initiated 
 by the sequence of instructions 
 
 (1) ATN 256+F 
 
 (2) SSR 58 
 
 (3) (Delay loop of 1 second) 
 
 (1) and (2) set the output side of SR58 to the bit 
 
 configuration 256+F. The 256 (bit 4) selects analog output 
 
 and starts the tape recorder in the record mode. The bits 
 
 defined by F select one of the four sampling rates and its 
 
 associated filter. The delay loop (3) is provided to 
 
 allow stabilization of the recorder but, again, it is not 
 
 required. The. allowed values for F are: 
 
 for 40,000 samples per second with a 
 20 KHz low pass filter 
 
 1024 for 30,000 samples per second with a 
 
 15 KHz low pass filter 
 
 512 for 20,000 samples per second with a 
 
 8.5 KHz low pass filter 
 
 1536 for 10,000 samples per second with a 
 
 4 KHz low pass filter 
 
50 
 
 Each output sample is transmitted by the sequence 
 
 (1) ATN M 
 
 (2) SSR 54 
 
 (1) and (2) store the number M or the contents of modi- 
 fier M into SR54. Since the program is prevented from 
 executing the SSR 54 instruction until a new sample is 
 requested by the interface, no other signal need be 
 tested. It is only necessary that the program be capa- 
 ble of executing this sequence at a rate exceeding the 
 sample conversion rate. The Illiac II will then stop 
 the program before each execution until the interface is 
 ready to receive a new value. 
 
 Analog output is terminated by the same sequence re- 
 quired by analog input. It should be noted that when 
 either bit 4, 5, or 7 (weights 256, 128, and 32 respect- 
 ively) is set to 1 in the output side of SR58, the re- 
 corder cannot be operated manually. Therefore, it is nec- 
 essary to make sure SR58 is set to after analog I/O is 
 terminated. 
 
 3.3. Error Checking 
 
 The error flag, set as described in Section II. 1, is 
 read by the sequence: 
 
 (1) ASN 58 
 
 (2) CAM M 
 
 (1) and (2) store in modifier M the input side of SR58 
 which has the value 0, if no errors have been detected, or 
 
51 
 
 1, if one or more errors have been detected. Execution 
 of (1) also causes the error flag to be reset to immedi- 
 ately and the input side of SR58 to be reset at the be- 
 ginning of the next sample period. Note that if (2) is 
 replaced by the instruction ADM M, modifier M becomes an 
 error counter. 
 
 B.4. Floating Point Conversion 
 
 The digitized samples may be easily converted to or 
 from normalized floating point by the following sequences: 
 
 (1) ATN Mx 
 
 (2) CAD 10,3,0 
 
 (3) STF FY 
 
 Sequence (1) , (2) stores the sample in modifier Mx 
 
 into the accumulator as a signed floating point number with 
 
 12 
 a magnitude <_ 0.9997558 (the value of £ 2" 1 ). The in- 
 
 i=l 
 struction (3) shifts the accumulator and stores it in fast 
 
 register FY so that the first modifier of FY (MO, M4 , M8 , 
 or M12) contains those bits of the original number with 
 weights 2 , 2" , . . . , 2~ . If the accumulator had a magni- 
 tude of < 0.999.7558 (as produced by the sequence (1), (2)) 
 the result in the first modifier would be the equivalent 
 sample value. Accumulator values with magnitudes >_ 1.0 
 will cause overflow to be set when (3) is executed. Thus 
 sample values in the range -4095 to +4095 may be mapped 
 directly into the normalized floating point indicated above 
 
52 
 
 and conversely. 
 
 Information regarding the programming to tape, disk 
 and drum I/O is given in bibliography references 2, 4, and 
 
 8. 
 
53 
 
 APPENDIX C. ADSYS2 TAPE FORMAT AND COMMAND LANGUAGE 
 
 DESCRIPTIONS 
 
 The reader should be familiar with Section II. 3 of 
 this thesis before attempting to read the following in- 
 formation. 
 
 C.l. File Tape Format 
 
 All records written on the user's file tape must be 
 256 Illiac II words in length. The first record on the 
 tape is the tape label record, and the first word of the 
 tape label record contains the 6 character BCD name 
 "ANALOG" in quarter words 0, 1, and 2 as a means of iden- 
 tifying the tape as a proper file tape. Quarter word 3 
 contains a binary "tape number" that may be used to 
 uniquely identify the tape. The only restriction on the 
 tape number is that it should lie in the range to 4095. 
 (Note that the tape number in no way refers to the logical 
 number of the tape unit on which it is mounted for process- 
 ing.) The remaining 255 words of the tape label record, 
 as well as the entire contents of any record following up 
 to the first tape mark (end-of-file) , may be specified by 
 the user and used for further labeling information if de- 
 sired. 
 
 Following the tape label record (and any additional 
 records), are an unspecified number of data files. At the 
 beginning of each data file there is a tape mark followed 
 by a file label record or another tape mark. The first 
 
54 
 
 tape mark serves to separate the data files while the 
 second tape mark, in place of a file label record, in- 
 dicates that there are no more data files beyond this 
 point. 
 
 The first word of each file label record serves to 
 uniquely identify the file. Quarter word contains a 
 binary number while quarter words 1, 2 and 3 are required 
 to be zero. The binary number is used to define the file 
 and may have any value from to 4095. The files need 
 not be numbered in increasing numeric order; however, no 
 two files on the same tape should have the same file 
 number. 
 
 Following the file label record are an unspecified 
 number of data records which constitute the file. A file 
 is terminated by the tape mark at the beginning of the 
 next sequential file. Samples in the data records are 
 stored one per quarter word, 102 4 per record. Sequencing 
 of the samples in time is from quarter word to 3 , word 
 to 255 with the records sequenced in the order that they 
 are read or written. 
 
 C.2. Conversion Tape Format 
 
 The conversion tape is copied from or onto the file 
 tape using multiple block records and is used for the 
 actual analog I/O. All records on the conversion tape 
 are 1024 Illiac II words long. The first record is pre- 
 ceded by a tape mark (written at the beginning of the tape) 
 
55 
 
 and the last record is followed by two tape marks. There 
 are no labels to be checked, and thus all the records are 
 data records. Sequencing of the samples in time is from 
 quarter word to 3, word to 1023 with the records 
 sequenced in the order they are read or written. (Note: 
 The conversion tape is to be considered a scratch tape 
 and should not be used to save data between runs. Further- 
 more, processing of the multiple block records may not be 
 performed during normal batch processing.) 
 
 C.3. The ADSYS2 Command Language 
 
 ADSYS2 begins execution by printing on the console 
 teletype 
 
 ADSYS2 LOADED 
 and then proceeds to rewind and initialize the conversion 
 tape on channel 5, unit 0. When this has been accomplished, 
 ADSYS2 begins job processing until a request is made by the 
 operator to terminate execution. Each job is initiated by 
 ADSYS2 printing the message 
 
 SELECT JOB 
 followed by -cwc bell rings indicating the operator is to 
 type in a command. Information typed in at any other time 
 is ignored. In describing the commands symbolic parameters 
 will be used to represent the actual numeric values that 
 are inpuz. In certain cases these parameters may be elimi- 
 nated by deleting them from the end of the list causing 
 ADSYS2 to use a default value instead. The parameters and 
 
56 
 
 their default values are as follows: 
 
 In This is the logical number of the tape unit 
 containing the user's file tape. This unit 
 may not be connected to channel 5 , and is 
 therefore limited to the values 6, 7, 8, or 
 11. This parameter may not be deleted if 
 used by a command. 
 
 tn This is the tape number of a specified file 
 tape. (0<tn<4095) If tn is typed in as a 
 ncr.-zero number, the tape specified will be 
 checked for, or written with, a tape label 
 record containing this number. If tn is 
 deleted or equal to zero the tape number 
 will not be checked or a zero tape number 
 will be written. Note that in all cases 
 where checking is performed the first word 
 of the tape label record must contain the 
 BCD name "ANALOG" regardless of whether or 
 not the tape number is verified. 
 
 fn This is the file number of a specified file. 
 (0<fn<4095) If fn is deleted, fn = will 
 be assumed. 
 
 r This is the sampling rate desired for con- 
 version. The allowed values are 1, 2, 3, or 
 
57 
 
 4 for lOKHz, 20KHz, 30KHz or 40KHz respect- 
 ively. If r is deleted or zero, r = 4 will 
 be assumed. Note that ADSYS2 will attempt 
 to process any of the four possible sample 
 rates. However, for rates exceeding 35KHz, 
 the run will be terminated immediately after 
 starting due to the insufficient data I/O 
 rate capability of the digital tape units. 
 
 t This is the maximum time limit for conver- 
 sion in seconds. (0<t<9 99) If t is deleted 
 or set to zero, no time limit is imposed. 
 
 f This is the frequency in hertzians of a 
 
 tone to be generated internally by ADSYS2. 
 (100<f<4000) If f is deleted or set to zero 
 f = 1000Hz will be assumed. 
 
 The commands which may be input to ADSYS2 are defined 
 as follows: 
 
 (1) COMMAND: LABEL In tn 
 
 ACTION: Rewind the tape on logical tape unit 
 In and write a tape label record with 
 the tape number tn followed by two 
 tape marks. All previous information 
 on the tape will be effectively de- 
 „. stroyed. When the job is completed, 
 reply with the message "JOB DONE". 
 
58 
 
 (2) COMMAND; 
 ACTION: 
 
 (3) COMMAND 
 ACTION : 
 
 LOAD In fn tn 
 
 Rewind the file tape on logical tape 
 unit In and check the tape label 
 record for validity. Then search the 
 tape until the file numbered fn is 
 found. Copy the data records from the 
 file tape onto the conversion tape 
 four at a time until a tape mark is 
 read, then rewind both tapes. The 
 previous contents of the conversion 
 tape are destroyed. When the job is 
 completed, reply with the message 
 "JOB DONE". (Note that if the number 
 of data records on the file tape are 
 not a multiple of 4, the last 1, 2, 
 or 3 records before the terminating 
 tape mark will not be copied onto the 
 conversion tape) . 
 SAVE In fn tn 
 
 Rewind the file tape on logical tape 
 unit In and check the tape label re- 
 cord for validity. Then search the 
 tape until the file numbered fn is 
 found. If file fn is not found, 
 create a new file labeled fn at the 
 end of the last, ^ile on the tape. 
 
59 
 
 Copy the data records from the con- 
 version tape onto the file tape until 
 a tape mark is read. Then, rewind 
 the conversion tape, write two tape 
 marks on the file tape, and rewind the 
 file tape. The previous contents of 
 the specified file and all following 
 files will be destroyed. When the job 
 is completed, reply with the message 
 "JOB DONE". 
 (4) COXMAND: A/D r t 
 
 ACTION: Rewind and write a tape mark at the 
 
 beginning of the conversion tape; then 
 reply with the message "READY". The 
 previous contents of the conversion 
 tape will be destroyed. When the 
 operator turns bit of SR2 8 from OFF 
 to ON, begin analog input at the sampl- 
 ing rate r for the time t. After each 
 data record is written on the conversion 
 tape, check for a possible termination 
 condition. If one is found stop analog 
 input, write two tape marks on the con- 
 version tape and rewind it, then reply 
 with the message "XXX END YYY ZZZ". 
 XXX is the type of termination and may 
 
60 
 
 (5) COMMAND: 
 ACTION: 
 
 be one of the following: 
 
 OPR if the operator sets bit of 
 SR2 8 to the OFF position. 
 
 TIME if the input time exceeds that 
 specified by t. 
 
 EOT if the physical end of the con- 
 version tape is sensed. 
 
 ERR if the tape data transfer rate 
 is below the specified sampling 
 rate. 
 
 YYY is the actual time expended in the 
 conversion in seconds (if >999, YYY will 
 equal 9 99) and ZZZ is the number of 
 records written in which one or more 
 conversion errors occurred. ZZZ is not 
 printed if it is zero. 
 
 D/A r t 
 
 Rewind and skip the tape mark at the be- 
 ginning of the conversion tape. Then 
 reply with the message "READY". When 
 the operator turns bit of SR2 8 from 
 OFF to ON, begin analog output at the 
 sampling rate r for the time t. After 
 
61 
 
 (6) COMMAND: 
 ACTION : 
 
 each record is read from the conver- 
 sion tape, check for a possible termina- 
 tion condition. If one is found, .„s.top 
 analog output, rewind the conversion 
 tape, and then reply with the message 
 "XXX END YYY ZZZ". This code is identi- 
 cal to that which occurs for A/D except 
 that EOT is replaced by EOF if a tape 
 mark indicating the end of the input 
 file is sensed. 
 SINE f t 
 
 Prepare to generate a sinusoidal full- 
 scale analog output of frequency f at 
 a sample rate 40,000 Hz; then reply 
 with the message "READY". When the 
 operator turns bit of SR2 8 from OFF 
 to ON, begin analog output of the re- 
 quired tone. At the end of each cycle, 
 check for a possible termination con- 
 dition. If one is found, stop analog 
 output and then reply with the message 
 "XXX END YYY". This code is identical 
 to that which occurs for A/D except 
 that XXX is restricted to either OPR 
 or TIME, and no checking is done for 
 conversion errors. 
 
62 
 
 (7) COMMAND. 
 ACTION: 
 
 (8) COMMAND 
 ACTION : 
 
 RAMP f t 
 
 Identical to SINE except a sawtooth 
 tone is produced. 
 END 
 
 Output the message "BATCH REENTRY" 
 and then terminate ADSYS2 by return- 
 ing to the batch processing stream. 
 
 C.4. Error Massages 
 
 The following error messages may be output by ADSYS2 
 in response to a job request. In all cases the job will 
 not be run. 
 
 (1) MESSAGE: INVALID PARAMETERS 
 
 MEANING: The job name or one of the input parameters 
 is illegal. 
 
 (2) MESSAGE: TAPE ERRORS 
 
 MEANING: Repeated tape errors were detected during 
 
 tape or file label processing. (This could 
 indicate an improper file tape) . 
 
 (3) MESSAGE: BAD TAPE LABEL 
 
 MEANING: The tape label record did not contain the 
 BCD name "ANALOG" in the first word or the 
 label record was not there (i.e., a tape 
 mark was written instead) . 
 
 (4) MESSAGE: WRONG TAPE NUMBER 
 
 MEANING: Tape label number checking was requested and 
 the indicated tape 'Hid not contain the given 
 
63 
 
 tape number. 
 
 (5) MESSAGE: BAD FILE LABEL 
 
 MEANING: The last three quarter words of the first 
 word of a file label were not all zero. 
 
 (6) MESSAGE: FILE NOT FOUND 
 
 MEANING: The file requested to be loaded onto the 
 conversion tape was not found on the file 
 tape. 
 
 C.5. Other Operating Information 
 
 During analog input the first 1 second of analog tape 
 is bypassed without being input to allow for speed stabili- 
 zation. When input is terminated another 1 second is by- 
 passed before the recorder is stopped. The same procedure 
 is followed during analog output except that the bypassed 
 tape is erased. 
 
 For the commands which wait until the operator sets 
 bit of SR2 8 to begin, the operator may instead turn on 
 bit 1 causing the job to be deleted and the message "JOB 
 NOT RUN" to be printed. 
 
 If an error is made in typing a command, typing the 
 character % will delete the line and send out two bell 
 rings indicating a new command is requested. 
 
 The total time charged is the sum of the times given 
 by the messages "XXX END YYY ZZZ" plus 3 minutes for over- 
 head. 
 
64 
 
 APPENDIX D. ADPAK2 SUBROUTINE CALLING SEQUENCES 
 
 The reader should be familiar with section II. 3 of 
 this thesis and with the use of FORTRAN and/or NICAP in 
 the Illiac II batch processing system before attempting 
 to read the following information. 
 
 D.l. Program Requirements 
 
 ADPAK2 is 4 72 locations long and uses the first 256 
 words of common storage as a tape I/O buffer. ^he common 
 locations may be used by the program between calls to 
 ADPAK2 subroutines. Any call to an ADPAX2 subroutine 
 destroys the contents of the accumulator and fast registers 
 and 1. East registers 2 through 7 are left unchanged. 
 
 The logical tape units used may be on either channel 
 4 or 5 but must be units that are normally allowed to the 
 user. Uncorrectable tape errors occurring during reading 
 or writing of data records will not cause program termina- 
 tion . 
 
 D.2. FORTRAN Calling Sequences 
 (I) STATEMENT: CALL ADLBL (I, J) 
 
 ARGUMENTS: Input - I, J; output - none 
 ACTION: Rewind logical tape I and write a tape 
 label record with the tape number J 
 followed by two tape marks. All pre- 
 vious data files on tape I are effec- 
 tively destroyed. 
 
65 
 
 ( 2 ) STATEMENT 
 ARGUMENTS 
 ACTION : 
 
 (3) STATEMENT 
 ARGUMENTS 
 ACTION: 
 
 CALL ADBGI (1,11, J) 
 Input - I,J,N; output - none 
 Rewind logical tape I and check the tape 
 label record for validity. If J ^ 0, 
 check to see that the tape number is the 
 same as J; otherwise, do not check the 
 tape number. After the tape label is 
 checked, search the tape for a file 
 numbered N and position the tape to read 
 the first data record from the file (the 
 input file is now active;) then, return 
 to the calling program. 
 CALL ADBLI (A,K) 
 
 Input - none; Output - A(1024),K 
 If the input file is not active, set 
 K = and return immediately to the call- 
 ing program. Otherwise, read the next 
 data record from the input file. If this 
 is not a tape mark, convert the 10 24 
 samples to floating point and store them 
 in the array A from A(l) to A(1024). Set 
 K = -1 or 1 if uncorrectable tape errors 
 were or were not encountered, respectively; 
 then, return to the calling program. If 
 the data record is a tape mark rewind the 
 input file tape, (the input file is now 
 
66 
 
 ( 4 ) STATEMENT 
 ARGUMENTS 
 
 ACTION : 
 
 (5) STATEMENT 
 ARGUMENTS 
 ACTION: 
 
 (6) STATEMENT 
 ARGUMENTS 
 ACTION - 
 
 inactive) set K = 0, and then return to 
 the calling program. 
 CALL ADSKI (M,K) 
 Input - M; Output - K 
 
 If the input file is not active set K = 
 Z and return immediately to the calling 
 program. Otherwise, skip over the next 
 M records in the input file. If no 
 ■cape mark is detected, set K = -1 or 1 
 .. f uncorrectable tape errors were or 
 were not encountered, respectively; then, 
 return to the calling program. If a 
 -cape mark is read, rewind the input file 
 cape, (the input file is now inactive) 
 set K = 0, and then return to the calling 
 program. 
 CALL ADEDI 
 None 
 
 If the input file is not active, return 
 immediately to the calling program. Other- 
 wise, rewind the input file tape, (the in- 
 put file is now inactive) then return to 
 the calling program. 
 CALL ADBGO (I,N,J) 
 Input - I,J,N; Output - None 
 Rewind logical tape I and check the tape 
 
67 
 
 ( 7 ) STATEMENT : 
 ARGUMENTS : 
 ACTION: 
 
 label record as for ADBGI, then search 
 the tape for a file numbered N. If the 
 file is found, position the tape to 
 write the first data record of the file. 
 Otherwise, write a new file label record 
 after the last file on the tape; (in 
 either case the output file is now active) 
 then, return to the calling program. 
 CALL ADBLO (A,K) 
 Input - A(1024); Output - K 
 If the output file is not active, set K 
 = and return immediately to the calling 
 program. Otherwise, convert the 1024 
 floating point samples in the array A 
 from A(l) to A(1024) into a data record 
 and write this onto the output file as 
 the next sequential data record. If the 
 end-of-tape indicator is not sensed, set 
 K = -1 or 1 if uncorrectable tape errors 
 were or were not encountered, respectively; 
 then, return to the calling program. If 
 the end-of-tape indicator is sensed, write 
 two tape marks and rewind the output file 
 tape. (The output file is now inactive.) 
 Set K = 0, and then return to the calling 
 program. 
 
68 
 
 (8) STATEMENT: CALL ADSKO (M,K) 
 
 ARGUMENTS: Input - M; Output - K 
 
 ACTION: If the output file is not active, set 
 
 K = and return immediately to the call- 
 ing program. Otherwise, write M records 
 of all zeros onto the output file. If 
 the end-of-tape mark is not detected set 
 K = -1 or 1 if uncorrectable tape errors 
 were or were not encountered, respect- 
 ively; then, return to the calling pro- 
 cram. If the end-of-tape indicator is 
 sensed, write two tape marks and rewind 
 ■ the output file tape. (The output file 
 is now inactive.) Set K = 0, and then 
 return to the calling program. 
 CALL ADEDO 
 None 
 
 If the output file is not active, return 
 immediately to the calling program. Other- 
 wise, write two tape marks and rewind the 
 output file tape; (the output file is now 
 inactive) then, return to the calling pro- 
 gram. 
 
 P. 3. KICAP Calling Sequences 
 
 NICA? programs may call any of the FORTRAN callable sub- 
 
 (9) STATEMENT 
 ARGUMENTS 
 
 ACTION: 
 
69 
 
 routines as follows: 
 
 CALL NAME 
 
 DECQ W,X,Y,Z 
 where name is the subroutine name, and W,X,Y, and Z are 
 the addresses of the input parameters required. For ex- 
 ample, to call AD3GI in NICAP, the sequence 
 
 CALL ADBGI 
 
 DECQ I,N,J,0 
 is used where I,N, and J are the addresses of the logical 
 tape number, file number, and tape number, respectively. 
 
 In addition, there are four other subroutines avail- 
 able only to NICAP programs, The calling sequences for 
 these are: 
 
 CAM 0,A 
 
 CALL ADBI1 (or AD301) 
 
 CAM 0,M 
 
 CALL ADSI1 (or ADS01) 
 ADBI1, ADBC1, ADSI1 and ADS01 are the same as ADBLI , ADBLO, 
 ADSKI, and ADSKO, respectively, where A is the address of 
 the first location of the array and M is the number of 
 records to skip. On return modifier zero equals the value 
 (not the address) of K. 
 
 D.4. Error Exits 
 
 If an error is detected by an ADPAK2 subroutine, a 
 message wil.1 be printed on the user 1 ? output, and SYSERR 
 
70 
 
 will be called. The form of the message is: 
 
 *** ADPAX2 ERROR - XXX *** 
 where XXX is one of the following: 
 
 (1) MESSAGE: ABLBL or ADBGO ATTEMPTED ACCESS OF INPUT 
 
 TAPE 
 MEANING: A call to ADL3L or ADBGO specified a logical 
 tape unit which contains a currently active 
 input file tape. 
 
 (2) MESSAGE: ABLBL or AB3GI ATTEMPTED ACCESS 0? OUTPUT 
 
 CAPE 
 MEANING: A call uo ADL3L or AD3GI specified a logical 
 tape unit which contains a currently active 
 output file tape. 
 
 (3) MESSAGE: TAPE ERRORS OR END-OF-TAPE DETECTED DURING 
 
 LABEL WRITING 
 
 or 
 TAPE ERRORS DETECTED DURING LABEL READING 
 Uncorrectable tape errors or an end-of-tape 
 indication occurred during tape or file 
 label record processing. 
 INCORRECT TAPE LABEL 
 
 The tape label record of a file tape did not 
 nave the 3CD name "ANALOG" in the first 
 three quarter words of the first word. 
 INCORRECT TAPE NUMBER 
 The tape number in the tape label record did 
 
 MEANING 
 
 (4) MESSAGE 
 MEANING 
 
 (5) MESSAGE 
 MEANING 
 
71 
 
 (6) MESSAGE: 
 MEANING: 
 
 not agree with that specified in a call to 
 
 ADBGI or ADBGO. 
 
 INCORRECT FILE LABEL 
 
 The last three quarter words of the first 
 
 word of a file label record were not all 
 
 zero. 
 (7) MESSAGE: REQUESTED FILE NOT FOUND 
 
 MEANING: The file number given in a call to ADBGI 
 
 was not found on the specified input file 
 
 tape. 
 In addition to the above, accumulator overflow or 
 specification of an illegal logical tape unit number may 
 cause the system to terminate the job. Accumulator over- 
 flow will occur if any of the parameters I,N,J, or M 
 (specified in D.2 and D.3) exceeds 4095, or if any sample 
 in the array A has an absolute value that is equal to or 
 greater than 1.0. 
 
72 
 
 BIBLIOGRAPHY 
 
 1. Gear, C.W. , Illiac II Manual; Use of the New Illinois 
 
 C ompute r Installation , University of 
 Illinois, Department of Computer Science, 
 Urbana, Illinois, March 19 63. 
 
 2. Gillies, D.B., Levin, M.S., Special Registers and In- 
 
 terrupts for the Illiac II , File No. 517, 
 University of Illinois, Department of 
 Computer Science, Urbana, Illinois, Decem- 
 ber 15, 1954. 
 
 3. Otis, A. 3., Jr., The Analog-Digital Programming System , 
 
 File No. 726, University of Illinois, De- 
 partment of Computer Science, Urbana, 
 Illinois, February 23, 1967. 
 
 4. Pisterzi, M.J. , Programming Aspects of the Magnetic 
 
 Tat>e Interplay Channels , File No. 5 88, 
 University of Illinois, Department of Compu- 
 ter Science, Urbana, Illinois, March 16, 
 1964. 
 
 5. Schroeder, M.R., Natural Sounding Artificial Reverber- 
 
 tion , Monograph 4309, Bell Telephone Labora- 
 tories, Inc., New York, N.Y., November 19 62. 
 
 6. Stephenson, B'.W., Analog-Digital Conversion Handbook , 
 
 Digital Equipment Corp., Maynard, Mass., 
 1964. 
 
 7. Susskind, A.K. , Notes on Analog-Digital Conversion Tech- 
 
 niques , The MIT Press, Cambridge, Mass., 
 1957. 
 
 8. Willard, R.E., Nuspl, S.J., Programming Aspects of the 
 
 Disk File Channel , File No. 620, University 
 of Illinois, Department of Computer Science, 
 Urbana, Illinois, August 2, 1965. 
 
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