Undocumented 8080 instructions?
cclist at sydex.com
Sat Dec 25 21:07:28 CST 2010
On 25 Dec 2010 at 17:18, dwight elvey wrote:
> It seemed like I recalled the NEC 8080's had some extras but it
> must have been brain rot on my part. I have one of their 8080's
> in my Poly88. It is quite easy to single step with this computer
> and display all the registers, memory pointed to by double
> registers and flags. I found nothing unusual happening on any
> of the other unused instructions. I have a newer AMD8080 I guess
> I could try some day.
I seem to recall that the problem with the NEC 8080 was somewhat
different treatment of the status flags. Apparently, NEC thought to
"improve" on the 8080's treatment of the flags. Good idea, but...
IMSAI let some of its early CPU boards out with the NEC CPU. Later,
I think they used up their stock of the NEC chips by using them in
their floppy controller.
Later revisions of the NEC 8080 (e.g. 8080AF) conformed with Intel's
I don't recall any added instructions, however.
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