|Design||CMOS, GaAs, ECL, SoS|
|Encoding||16 bit instructions|
|General purpose||16 × 16-bit|
|Floating point||Optional in specification|
MIL-STD-1750A or 1750A is the formal definition of a 16-bit computer instruction set architecture (ISA), including both required and optional components, as described by the military standard document MIL-STD-1750A (1980).
The 1750A supports 216 16-bit words of memory for the core standard. The standard defines an optional memory management unit that allows 220 16-bit words of memory using 512 page mapping registers (in the I/O space), defining separate instruction and data spaces, and keyed memory access control.
Most instructions are 16 bits, although some have a 16-bit extension. The standard computer has 16 general purpose 16-bit registers (0 through 15). Registers 1 through 15 can be used as index registers. Registers 12 through 15 can be used as base registers.
Any of the 16 registers could be used as a stack pointer for the SJS and URS instructions (stack jump subroutine and unstack return subroutine), but only register 15 was used as the stack pointer for the PSHM and POPM instructions (push multiple and pop multiple).
The computer has instructions for 16, and 32-bit binary arithmetic, as well as 32 and 48 bit floating point. I/O is generally via the I/O instructions (XIO and VIO), which have a separate 216 16-bit word address space and may have a specialized bus.
Because MIL-STD-1750A did not define implementation details, 1750A products are available from a wide variety of companies in the form of component, board, and system-level offerings implemented in a myriad of technologies, often the most advanced and exotic of their respective periods (e.g. GaAs, ECL, SoS).
Of particular interest is the fact that 1750A systems often offer very high levels of radiation and other hazardous environment protection, making them particularly suited for military, aviation and space applications.
Examples of MIL-STD-1750A implementations include:
- GEC-Plessey RH1750, a radiation-hardened version for aerospace and space flight applications. GEC-Plessey, under its previous incarnation as Marconi Electronic Devices, also initially developed the MAS281 and MA31750A series of processors, later made available through Dynex Semiconductor
- Honeywell HX1750, fabricated on Honeywell's Silicon on Insulator CMOS (SOI-IV) process giving radiation hardness. The HX1750 includes an FPU and peripherals on chip.
- CPU Technology, Inc. CPU1750A-FB, a high performance 1750A SOC designed to give existing applications a late life performance boost.
- Pyramid Semiconductor PACE P1750A. The family includes the P1750A CPU, the P1750AE Enhanced CPU, the P1753 Memory Management Unit (MMU), the P1754 Processor Interface Chip (PIC) and the P1757ME Multi-Chip Module. This line was acquired from Performance Semiconductor in 2003.
- National Semiconductor F9450 series.
- Marconi Electronic Devices MIL-STD-1750A.
- Royal Aircraft Establishment Farnborough MIL-STD-1750A implementation in AMD 2901 bit-slice technology. 
- Johns Hopkins University Applied Physics Laboratory (JHU/APL) MIL-STD-1750AAV space flight qualified processor. A multi-board silicon on sapphire implementation specifically designed for space flight.
- Dynex Semiconductor MAS281. A radiation hardened SOC implementation on a 64-pin multichip module with an optional MMU.
Processors based on MIL-STD-1750A are usually programmed in JOVIAL, a high-level programming language defined by the United States Department of Defense which was derived from ALGOL 58. To a lesser extent, Ada was used.
In addition, DDC-I provides its SCORE Integrated Development Environment (IDE) with both Ada95 and C compilers, and TADS (Tartan Ada Development System) Ada83 development environment, both targeting processors based on MIL-STD-1750A.
The U.S. Air Force defined the standard in order to have a common computing architecture and thereby reduce the costs of software and computer systems for all military computing needs. This includes embedded tasks such as aircraft and missile control systems as well as more mundane general military computing needs.
The advantages of this concept were recognized outside of the USAF and the 1750A was adopted by numerous other organizations, such as the European Space Agency, NASA, Israeli Aircraft Industries and many projects in academia.
Examples of military aircraft using the 1750A include:
- USN F-18 RFCS Flight Control Computer
- USAF F-16 Digital Flight Control System and Fire Control Computer
- US Army AH-64D Apache Longbow Helicopter
- IAI Lavi fighter
- IBM Federal Systems AP-102 Avionics Computer (used in various roles including the USAF F-111 avionics upgrade)
Use in space
Fully space rated implementations make the 1750A one of the few types of computers that are applicable for use in deep space applications. Example spacecraft that use the 1750A are:
- EOS Aqua, Aura and Terra
- ESA Cluster
- ESA Rosetta
- ESA Envisat - Envisat's ASAR instrument, built by Matra Marconi Space and comprising the Central Electronics Sub-Assembly and Antenna Sub-Assembly used a total of 42 GEC-Plessey MA31750A processors in a dual-redundant configuration
- MSTI-1, 2 and 3
- NASA Cassini
- NASA Landsat 7
- NASA Mars Global Surveyor
- Naval Research Laboratory Clementine Lunar Orbiter
- USAF Titan-4 Guidance Computer
- NOAA GOES-13, GOES-O and GOES-P
- Midcourse Space Experiment (MSX) spacecraft developed at JHU/APL
- ISRO Space Recovery Experiment-1 Guidance and Navigation Computer
|This section does not cite any references or sources. (October 2013)|
With the release of the Notice 4 revision to the standard on July 31, 1996, MIL-STD-1750A was declared inactive for new military projects in the USA. However, both the Indian Space Research Organisation (ISRO) and the Chinese aerospace industry continue to use the 1750 for new projects.
To necessarily say the CPU is technologically defunct can be nebulous. This CPU can run at 0.5 MIPS to 3 MIPS depending on the operating speed (from 1 MHz to 20 MHz). The lack of modern floating point capabilities makes this CPU less suitable for some (but not all) modern embedded applications. However, lack of familiarity (and modern compiler support) with this CPU makes its uptake in the civilian computing sector difficult.
More modern CPUs like the Mongoose-V (used on the New Horizons spacecraft) and the higher performance RAD750 that are both based on more modern computer architectures are replacing the MIL-STD-1750A in the space sector over time. It is expected that by 2030 this CPU's use in aerospace may cease.
- Software Vendor Information
- Specification and vendor information
- Ada and ANSI C compilers
- MIL-STD-1750A, 2 July 1980, with updated Notice 1, 21 May 1982
- FlightLinux Project Target Architecture Technical Report References to use in spacecraft
- DODSSP U.S. Department of Defense Single Stock Point for Military Specifications, Standards and Related Publications
- Dynex Semiconductor MA31750 Processor
- Pyramid Semiconductor P1750A-SOS Processor