NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

8085 Microprocessor

"Back to the Moon: The Verification of a Small Microprocessor's Logic Design"

Seminar: presented by Hugh Blair-Smith

Presentation: Back to the Moon

Paper: (.doc)  --  (.pdf)
27th Digital Avionics Systems Conference
October 26-30, 2008

The original and primary task of self-test program Smalley3 was independent verification of the logic design of the LOLA DU (Lunar Orbiter Laser Altimeter Digital Unit) micro­processor. Tasks were added to verify continuing correct operation of this central processing unit (CPU) under margin testing for supply voltage, ambient temperature, and clock frequency.  Finally, an on-orbit diagnostic task was added so that any malfunctions of LOLA in lunar orbit can be identified as faults in, or not in, the CPU.
     The Lunar Reconnaissance Orbiter space­craft will be launched to the Moon in 2009 with six scientific instruments including LOLA, each containing an embedded microprocessor to perform real-time subsystem control calcula­tions.  LOLA's CPU is a small, custom-designed processor, designed to meet the mission require­ments while minimizing resources. This 8-bit machine is essentially code compatible with Intel's 8085 but is implemented in modern technology, an advanced, radiation-hardened 0.15 µm gate array, with the only logic element types being a 4:1 multiplexor and a flip-flop.
     This paper explains the fundamental structure of the verification task, shows how particular instructions are verified, presents a high-coverage scheme for detecting inadvertent RAM alteration, describes subsystem testing of RAM, and reviews the results of the verification effort.  Some infamous CPU design flaws from both the commer­cial industry and aerospace flight control systems are discussed.

On-Board Software for the Mars Pathfinder Microrover

Jack Morrison and Tam Nguyen
Second IAA International Conference on Low-Cost Planetary Missions
Laurel, MD - 1996


The Pathfinder Micro-rover Flight experiment will perform engineering and science experiments on the Martian surface to pave the way for future Mars missions. The rover is controlled by a 1970's era microprocessor. Its on-board software, while in some ways a typical embedded-system design, has to deal with some unusual constraints.

The rover will be operating in a harsh and mostly unknown environment, with limited electrical and processing power, accessible only via a limited-bandwidth communication link with long time delays. The software design is driven by these factors to provide reliability in the face of hardware, software, and operational failures, flexibility to allow adaptation and reconfiguration, simplicity, predictability, and visibility into its internal state and the external environment.

This paper describes the overall software structure, and details some of the more interesting features of the design, including error handling, power control logic, and navigation with hazard avoidance. The development environment is also described, including the use of world-wide-web- style hypertext to provide quick access to the collection of documents that accumulate in a software project.

80C85RH-8 Total Dose Radiation Test

October 1989


Testing Summary

The 80C85RH-8-retains its integrity up to 200K Rads. Above 200K Rads there is a decline in the electrical performance of the component. I would not recommend using it above 200K Rads (si).



Products by chip - Intel 8 bitXL


8085 Simulator IDE with BASIC Compiler, Assembler, Disassembler and Debugger


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