D-17B

Autonetics D-17 guidance computer from a Minuteman I missile.

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 (28 kg), contains 1,521 transistors, 6,282 diodes, 1,116 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 1960s 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.

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 (microseconds): 78 1/8

Multiply (µs): 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 (µs): 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 (rxcluding storage access):

Add: 78 µs

Multiply: 1,016 µs

Construction (arithmetic unit only): transistor-diode logic is used.

Timing: Synchronous

Operation: Sequential

Storage

Medium	No. of Words	Access (µs)
Rotating disk	2,688	5,000 avg.	(gen. purp. channels)	Rotating disk	41		(rapid access poops)			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 ms   (Program Control)
   Phase - Voltage       (Program Control)

28 digital lines (output) 12 analog lines (output) 13 pulse lines (output) 25,600 word/s 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 (28 kg)

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 (44 L)

Weight, computer: 70 lb (32 kg)

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

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
40 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 70, 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

D-17B computer architecture block diagram.

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.

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 709 mainframe computer.^[1]

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.^[2]

The MM II missile was deployed with a D-37C disk computer. Autonetics also programmed functional simulators and the code inserter verifier that was used at Wing headquarters to generate and test the flight program codes to go into the airborne computer.^[3]

Notes

1. ^ 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
2. ^ Lin, Pp. 491-509
3. ^ Lin, Pp. 491-509

References

• Autonetics Division of North American Rockwell. Inc.; Minuteman D-17 Computer Training Data. Anaheim, California, 8 June 1970.
• Autonetics Division of North American Rockwell. Inc.; Part I - Preliminary Maintenance Manual of the Minuteman D-17A Computer and Associated Test Equipment. P.O. Memo 71. Anaheim, California, 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.
• Lin, Tony C.; "Development of U.S. Air Force Intercontinental Ballistic Missile Weapon Systems." Journal of Spacecraft and Rockets, vol. 40, no. 4, 2003. Pp. 491-509.
• Weik, Martin H.; A Fourth Survey of Domestic Electronic Digital Computing Systems. Ballistic Research Laboratories, Aberdeen Proving Ground, MD, Report No. 1227, January 1964.

See also

• D-37C
• Minuteman (missile)