Revision as of 02:06, 25 December 2015

TMX1795 Developer Texas Instruments Transistors ~3,000 Clock Unknown Bus Width 8-bit Memory Specs Packaging

The TMX1795 was a working prototype for an 8-bit microprocessor designed by Texas Instruments in 1970-1971. The 1795 was architecturally very close or not identical to that of Intel's 8008.

History

Datapoint Corporation, then Computer Terminal Corporation (CTC), was looking to create a more powerful machine in mid-1969. CTC was convinced that to achieve that they would need to create a more complex integrated circuit as using discrete logic would not meet their desired specifications. After having the basic architecture for that device thought up, CTC arranged a meeting with Bob Noyce, President of Intel and the President of Texas Instruments to discuss the device concept. Each one was given a pre-drawn basic schematic of the device.

Intel had a working specs for the 8008 by January or February of 1970^[1]. While it is unknown how much of the Intel specs TI got to see from CTC, Ted Hoff claimed that it's clear they've copied a fair bit pointing out that initially the 8008 had a bug with the RESTART instruction which should switch execution to the interrupt handler and execute CALL to save the stack point. In the original plans this part was missing - same was true with Gary Boone's patent.

It was a little-- well, there were ways, but the difference was that the TI chip did not change the restart instruction from a jam load to a call. We made the restart a call, so you could use that single byte instruction for the interrupt, and they did not have it. But at least in one of their patents they argue that you use the restart to implement an interrupt. Which means you just wiped out the status of the processor.

Ted Hoff^[1]

This bug was, however, corrected later in the final design of Intel's 8008. Boone has however denied the allegation and said that while they were told Intel has been doing considerably better, no proprietary information was ever given to them.

Yeah, but there's not a question that even in 1970, '71 it was a race. I mean, really, I mean, if you look at TI, for example, we helped them it looks like. It looked like, but still they were developing an eight-bit processor which was essentially the 8008. And they came out in April/May timeframe with that product. We heard-- I heard from Vic Poor that it never worked. But TI claims that it did work. In any event, whether it worked or not, it was later than the 4004 by one or two months. That tells you how much execution was important to being first in the market.

Federico Faggin^[1]

Museum displays

• TMX1795NS, Computer History Museum

References

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