There is quite a story behind the RCA 1802 ‘COSMAC’ processor which we used for the various low power designes in the early ‘80s!
The original design by Joe Weisbecker in the early 1970s in TTL logic (over 100 discrete logic chips!) as the basis of a home computer system. He described the home computer he built with the processor in 1974 and tested with his children – 3 years before the Apple II appeared.
RCA took Weisbecker’s design into a 2 chip processor in 1975 and then in single chip form as the 1802 in 1976. It was the first processor to be made using CMOS technology. The advantage of CMOS over the more common NMOS used by Intel and others was ultra low power consumption. Also, a radiation hardened version was produced and 6 of these were used in the Galileo probe launched in 1989 which orbited Jupiter between 1995 and 2003 – the first microprocessor in space! It is also used in the Hubble Space Telescope.
The wide temperature range of the standard chip (military versions had an even wider range) meant it could be used in vehicles and in 1980 was used by Chrysler and others in engine control systems. Low power consumption opened up new markets such as the ones we were considering – Plessey Payphones for example used it as it could be entirely powered through the phone line.
The early, simple design however meant the processor had limitations compared with the more common Intel and Motorola designs. No real conditional branching, no stack and no subroutine support. However, it did have 16 16-bit registers and these could be used to good use. Frustrating for programmers used to other microprocessors!
RCA released a number of different systems based on the processor family (expanded versions appeared as 1804 etc) and we used one available in the UK – the Microboard Computer Development System (MCDS). The Microboard range consisted of a series of boards which could be used on a common bus / backplane. We felt the cost of these would be prohibitive for the markets we were approaching so later we designed our own – the 1470 range.
Back to 1983