* Posts by kenshirriff

2 posts • joined 9 Feb 2016

Picking apart the circuits in the ARM1 – the ancestor of your smartphone's brain

kenshirriff

Strangely enough, the 8008 architecture is a copy of the processor in the Datapoint 2200 programmable terminal, which contained a CPU built from 7400-series TTL chips. The 8008 was intended to replace this hardwired processor, but ended up being sold as a separate processor. For some reason, Intel doesn't publicize this much. You can trace Intel's little-endian architecture back to the serial processor in the Datapoint 2200 - when you're adding one bit at a time, you want to start with the lowest. That's also why the 8008 and descendants generate a parity flag - it's very useful for a terminal.

The 4004 has a totally different architecture, and the 8008 is not based on it at all. The 8008 of course led to the 8080, 8085 and Z-80. Going to 8086 was a bigger jump - as an earlier post mentioned, 8080 assembly could be sort of translated to 8086 code. One interesting thing about the 8085 is it implemented instructions that were never documented because Intel decided they didn't want to have to support them in the 8086. Well, enough random chip facts.

kenshirriff

Re: No mention that the original design files were found and are visualised on the web!

Yes, the Visual 6502 team should definitely get credit for obtaining the ARM1 layout and building a simulator - my reverse engineering is based on their data. Also Dave Mugridge has also been doing a lot of ARM1 reverse engineering and his website (daveshacks.blogspot.com) is worth visiting.

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