How the 8086 processor's microcode engine works

Re:How the 8086 processor's microcode engine works by EvanAnderson on Saturday December 03, 2022 @08:57PM (#33849751)

I had a laptop w/ a NEC V30 (an Ultralite PC-17-02[0]) and I recall it being a very peppy machine even compared to my father's 286. I did some assembly coding on it and I liked having the 286 PUSHA/POPA instructions. I didn't know about the 8080 emulation mode that it has, too, and it kinda makes me wish I had one to play with now.

I had absolutely no idea re: the LinnDrum being a PC. That's really cool. I've never seen one in the flesh, but now I'm wondering if anybody has done conservation of the firmware. It would be a lot of fun to look at the code.

[0] http://old.chuma.org/ultralite/index.shtml

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Re:How the 8086 processor's microcode engine works by rwmj on Sunday December 04, 2022 @09:47AM (#33854122)

Back in the day I tried running a CP/M program on the V30 alternate instruction set. It didn't work and I eventually tracked it down to the program using one of the Z80-only LDI/LDR/LDIR block instructions. You're not supposed to use those with CP/M but because CP/M ran on many UK Z80 machines like the Amstrads, inevitably real world programs did. The V30 would have been a great way to run Z80 software [in the late 1980s] if only they'd implemented these :-)

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Re:How the 8086 processor's microcode engine works by rasz on Sunday December 04, 2022 @10:39AM (#33854610)

Wouldnt undefined instruction trap take care of that?

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Re:How the 8086 processor's microcode engine works by rwmj on Sunday December 04, 2022 @11:10AM (#33854876)

Good question! Did V30 trap on undefined instructions?

8086 didn't according to https://retrocomputing.stackexchange.com/questions/11327/wha..., but V30 was more like an 80186 which did trap, but then 8080 emulation mode might have worked differently again.

Also I don't recall how I worked out that the extended Z80 instructions were causing the problem. Debugging was a lot more complicated in those days, although programs were also much smaller.

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Re:How the 8086 processor's microcode engine works by kens on Sunday December 04, 2022 @12:54PM (#33855906)

I took a look at the V30 manual and it doesn't have an undefined instruction trap. It's an interesting chip, a superset of the 8086 as well as 8080 emulation. It includes bit manipulation instructions kind of like the Z80, along with multidigit BCD arithmetic.

https://www.ceibo.com/eng/datasheets/NEC-V20-V30-Users-Manua...

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Re:How the 8086 processor's microcode engine works by rasz on Sunday December 04, 2022 @04:31PM (#33858122)

V33/V53 and V33A/V53A do have them, with non A variants as non standard exception 122 http://elm-chan.org/docs/dev/v53_e.html mentions it. They build a cute board around it in 1998 http://elm-chan.org/works/cpu_v53/report.html

according to MAME V40 has it as standard exception 6? https://github.com/lesbird/MAME4apple-037b5/blob/master/MAME... Then again https://forum.vcfed.org/index.php?threads/nec-v20-and-cp-m.7... says no.

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