D-17B
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The D-17B is a computer used in missile guidance systems, specifically the Minuteman I NS-1OQ missile guidance system, which contains a D-17B computer, the associated stable platform, and power supplies. The D-17B weighs approximately 62 pounds, contains 1521 transistors, 6282 diodes, 1116 capacitors, and 504 resistors. These components are mounted on double copper-clad, engraved, gold-plated, glass fiber laminate circuit boards. There are 75 of these circuit boards and each one has been coated with a flexible polyurethane compound for moisture and vibration protection. The high degree of reliability and ruggedness of the computer are evidenced by the strict requirements of the weapons system. Use of the D-17B is especially appropriate when high reliability is necessary under extreme environmental conditions such as high shock, acceleration, or vibration that preclude the use of other computers.
Since an airborne, computer-controlled missile only gets one chance to execute its mission, the design specifications of the D-17B required very high reliability. This was achieved by using DRL (diode-resistor) logic extensively and only using DTL (diode-transistor) logic where gain or inversion was required in this fully solid-state computer. In the early 1960's when the D-17B was designed, transistors were not as reliable as they are now, thus the designers used transistors only when necessary. The rotating disk memory, with non-destructive readout (NDRO), also enhanced the reliability of the computer. In actual, real-time situations involving Minuteman missiles, the mean time between failures (MTBF) was over 5.5 years.
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[edit] Specifications
Minuteman I D-17B Computer Specifications
YEAR: 1962
The D17B is a synchronous serial general-purpose digital computer.
MANUFACTURER
Autonetics Division of North American Aviation
APPLICATIONS
Guidance and control of the Minuteman I ICBM.
PROGRAMMING AND NUMERICAL SYSTEM
NUMBER SYSTEM: Binary, fixed point, 2's complement
LOGIC LEVELS: 0 or False, OV; 1 or True, -10V
DATA WORD LENGTH (bits): 11 or 24 (double precision)
INSTRUCTION WORD LENGTH (bits): 24
Binary digits/word: 27
Instructions/word: 1
Instruction type: One and half address
NUMBER OF INSTRUCTIONS: 39 types from a 4-bit op code by using five bits
of the operand address field for instructions
which do not access memory
EXECUTION TIMES:
Add (microsec): 78 1/8
Multiply (microsec): 546 7/8
or 1,015 5/8 (double precision)
Divide: (software)
(Note: Parallel processing such as two simultaneous single precision
operations is permitted without additional execution time.)
CLOCK CHANNEL: 345.6 Hz
ADDRESSING:
Direct addressing of entire memory
Two-address (unflagged) and three-address (flagged) instructions
MEMORY:
Word Length (bits): 24 plus 5 timing
Type: Ferrous-oxide-coated NDRO disk
Cycle Time (us): 78 1/8 (minimal)
Capacity (words): 5,454 or 2,727 (double precision)
INPUT/OUTPUT:
Input Lines: 48 digital
Output Lines: 28 digital
12 analog
3 pulse
Program: 800 5-bit char/s
Instruction word format:
+--------+--------+------+--------+---------+--------+--------+
| TP | T24 21 | 20 | 19 13 | 12 8 | 7 1 | 0 |
+--------+--------+------+--------+---------+--------+--------+
| Timing | OP | Flag | Next | Channel | Sector | Timing |
| | | | Inst. | | | |
| | | | Sector | | | |
+--------+--------+------+--------+---------+--------+--------+
Registers
Phase and voltage output registers
ARITHMETIC UNIT (Excluding Storage Access)
Add: 78 Microsec
Multiply: 1,016
Construction: (Arithmetic unit only) Transistor-diode logic is used.
Timing: Synchronous
Operation: Sequential
STORAGE
No. of Access
Medium Words Microsec
Rotating Disk 2,688 5,000 Avg. (Gen. Purp. Channels)
Rotating Disk 41 (Rapid Access Loops)
40 (1 word loop)
160 (4 word loop)
320 (8 word loop)
640 (16 word loop)
INPUT
48 digital lines (input)
26 specialized incremental inputs
-Medium- -Speed-
Paper/Mylar Tape 600 chars/sec
Keyboard Manual
Typewriter Manual
OUTPUT
-Medium- -Speed-
Printer Character 78.5 - 2,433 millisec (Program Control)
Phase - Voltage (Program Control)
28 digital lines (output)
12 analog lines (output)
13 pulse lines (output)
25,600 words/sec maximum I/O transfer rate
Physical characteristics
Dimensions 20 in. high, 29 in. diameter, 5 in. deep
Power- 28 VDC at 25 A
Circuits- DRL and DTL
Weight- 62 pounds
CONSTRUCTION:
Double copper clad, gold plated, glass fiber laminate,
flexible polyurethane-coated circuit boards
SOFTWARE:
Minimal delay coding using machine language
Modular special-purpose subroutines
RELIABILITY: 5.5 years MTBF
CHECKING FEATURES
Parity on fill and on character outputs
POWER, SPACE, WEIGHT, AND SITE PREPARATION
Power, computer 0.25 Kw
Air conditioner, Closed system
Volume, computer 1.55 cu ft
Weight, computer 70 lbs
Designed specifically to fit in cylindrical guidance package.
The word length for this computer Is 27 bits, of which 24 are used In computation. The remaining 3 bits are spare and synchronizing bits. The memory storage capability consists of a 6000 rpm magnetic disk with a storage capacity of 2985 words of which 2728 are addressable. The contents of memory include 20 cold-storage channels of 128 sectors (words) each, a hot-storage channel of 128 sectors, four rapid access loops (U,F,E,H) of 1, 4, 8, and 16 words respectively, four 1-word arithmetic loops (A,L,H,I), and a two 4-word input buffer input loops (V,R).
The outputs that can be realized from the D-17B computer are binary, discrete, single character, phase register status, telemetry, and voltage outputs. Binary outputs are computer generated levels of +1 or -1 available on the binary output lines.
 Heads of magnetic disc from a Minuteman I missile. |
 The rapid access loops |
 Magnetic disk: Top view |
 Magnetic disk: Bottom View |
[edit] Instruction set
D-17B Instruction Repertoire Numeric Code Code Description ------------ ---- ----------- 00 20, s SAL Split accumulator left shift 00 22, s ALS Accumulator left shift 00 24, 2 SLL Split left word left shift 00 26, r SLR Split left word right shift 00 30, s SAR Split accumulator right shift 00 32, s ARS Accumulator right shift 00 34, s SRL Split right word left shift 00 36, s SRR Split right word right shift 00 60, s CoA Character output A 04 c, S SCL Split Compare and .ivt 10 C, S TMI Transfer on minus 20 c, s SMP Split multiply 24 c, s MPY Multiply 30 c, s SMM Split multiply modified 34 c, s MPM Multiply modified 40 02, s BOC Binary output C 4o 10, s BCA Binary output A 40 12, s BOB Binary output B 40 20, s RSD Reset detector 40 22, s HPR Halt and Proceed 40 26, s DOA Discrete output A 40 30, s VOA Voltage output A 40 32, s VOB Voltage output B 40 34, s VOC Voltage output C 40 40, s ANA And to accumulator 40 44, s MIM Minus magnitude 40 46, s COM Complement 40 50, s DIB Discrete input B 40 52, s DIA Discrete input A 40 60, s HFC Halt fine countdown 40 7-, s LPR Load phase register 44 c, s CIA Clear and Add 50 c, s TRA Transfer 54 c, s STO Store accumulator 60 c, s SAD Split add 64 c, s ADD Add 70 c, s SSU Split subtract 74 c, s SUB Subtract
Special features of the D-17B computer include flag store, split-word arithmetic, and minimized access timing. Flag store provides the capability of storing the present contents of the accumulator while executing the next Instruction. Split-word arithmetic is used in performing arithmetic operations on both halves of a split word at the same time. A split word on the D-17B consists of 11 bits. Minimized access timing is the placing of instructions and data in memory so that they are available with minimum delay from the disk memory.
[edit] Guidance software
Autonetics was the associate contractor for the Minuteman (MM) guidance system, which included the flight and prelaunch software. This software was programmed in assembly language into a D17 disk computer. TRW provided the guidance equations that Autonetics programmed and was also responsible for the verification of the flight software. When MM I became operational, the flight computer was the only digital computer in the system. The targeting was done at Strategic Air Command (SAC) Headquarters by the Operational Targeting Program developed by TRW to execute on an IBM mainframe computer.[6]
Sylvania Electronics Systems was selected to develop the first ground-based command and control system using a programmable computer. They developed the software, the message processing and control unit for Wing 6. To support the deployment of the Wing 6 system, TRW, Inc. developed the execution plan program (EPP) from a mainframe computer at SAC and performed an independent checkout of the command and control software. The EPP assisted in assigning targets and launch time for the missiles.[6]
The MM II missile was deployed with a D-37C disk computer. Autonetics also programmed the code inserter verifier that was used at Wing headquarters to generate the codes to go into the airborne computer.[6]
[edit] References
- Minuteman D-17 Computer Training Data. Anaheim, California: Autonetics Division of North American Rockwell. Inc. 8 June 1970.
- Part I - Preliminary Maintenance Manual of the Minuteman D-17A Computer and Associated Test Equipment. P.O. Memo 71. Anaheim. California: Autonetics, Division of North American Rockwell, Inc., January 1960.
- Beck, C.H. Minuteman Computer Users Group, Report MCUG-l-71. New Orleans, Louisiana: Tulane University, April 1971.
- Beck, C.H. Minuteman Computer Users Group. D-17B Computer Programming Manual. Report MCUG-4-71. New Orleans. Louisiana: Tulane University, September 1971.
- Beck, Charles H. Investigation of Minuteman D-17B Computer Reutilization. Available from NTIS/DTIC as document AD0722476, January 1971, 54 pp.
- Tony C. Lin. Development of U.S. Air Force Intercontinental Ballistic Missile Weapon Systems. Journal of Spacecraft and Rockets, vol. 40, no. 4, 2003. Pp. 491-509.
- Martin H. Weik. A Fourth Survey of Domestic Electronic Digital Computing Systems. Ballistic Research Laboratories, Aberdeen Proving Ground, MD, Report No. 1227, January 1964. [1]
