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Eight More '8-Bit Era' Microprocessors

83 points by klelatti

by drfuchs

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I did some assembly programming on the Fairchild F8 mentioned in the prequel article. Quaintest feature: Doing a “long” jump (more than 127 bytes away) would cause the accumulator register to be clobbered. Presumably, there was nowhere else to store the high (low?) order address byte routing things around to the PC register. This was also a problem for the debugger (in ROM on the development system), since continuing from a breakpoint necessitated a long jump, so it couldn’t restore the accumulator. So, the debugger would just simulate instructions until it hit a jump, which it could then jump to. Or something like that. Fairchild provided a listing of the source to the debugger / emulator, and the line that simulated messing up the accumulator during single-stepping was commented “The F8 Touch!” It made an impression 50 years ago.

by nicole_express

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The Signetics 2650 found its way into a bunch of arcade games by lieu of British company Century Electronics. I have a conversion kit of theirs installed into a Donkey Kong Jr. board, which outright replaces DK Jr.'s Z80 with a daughterboard containing the CPU. Always wondered why they chose that in particular, it's not a very common chip, and just using the Z80 that was there and replacing the ROMs was the more common option for conversion kits like that.

by drmpeg

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The article kind of disses the Intel 8085. For those of us with 8080 code bases that were never going to be rewritten for the Z80, it was a welcome upgrade. On the paper dryer process control systems I was working on in 1979, the 8085 based Intel 80/30 Multibus SBC could be dropped in for the older 8080 based 80/20 SBC with no changes and provide a significant 2.5X performance upgrade.

by jhbadger

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The RCA-1802 was used in the COSMAC Elf computer which was described as a hobbyist project to build in a series of articles in Popular Electronics 50 years ago. The Elf may be obscure but one thing developed on it (or its successor, the COSMAC VIP), CHIP-8, lives on -- it was (by some definitions) the first "fantasy console" like Pico-8 and TIC-80 today -- a virtual machine designed for writing action games.
https://en.wikipedia.org/wiki/COSMAC_Elf https://en.wikipedia.org/wiki/CHIP-8

by anthk

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The 6809 was a little of a beast too. It powered the Vectrex and some TRS-80 Color models.
The OS was interesting too: https://en.wikipedia.org/wiki/OS-9

by repelsteeltje

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It's easy to forget how much innovation divergence was happening in the early 70s. Up till the late nineties we speculated that ISAs other than x86 (spec. RISC designs) would win in the end.
Imagine these 8 bitters were mostly hardwired, with less than a million transistors.

by fjfaase

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Question: I once heard somebody talk about a micro-controller (with a minimal instruction set) where every register could be the program counter. It did not have jump or call instructions. You had 'emulate' those with the instruction (possibly conditionally) that changed the assignment of the program counter to one of the instructions. If I am not mistaken, it had eight registers. Does this ring a bell?

by troad

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Slightly orthogonal, but I'm curious how much effort is going into capturing historic hardware in accurate FPGA representation?
There'll come a day when the final physical 6502, 80486 (etc etc) powers off for the final time, and it seems like these technologies would be worth preserving. (I'm sure this is much easier said than done, not trying to minimise the effort involved.)
Is there a project that does something like this?

by jccx70

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