Emulating older computers on modern, much faster systems, is very common nowadays – but how about emulating the Intel 8080 (1974) on a MOS 6502 system like the KIM-1 (1975)? The “8080 Simulator for the 6502” by Dann McCreary from 1978 does exactly that.
Why imitate one microprocessor with another? You probably purchased this 8080 simulator package to do one or more of the following:
The emulator is extremely size-optimized and fits in less than 1 KB of RAM. This was done by compressing the 256-entry opcode space into 25 sections of similar instructions that could be handled by one generic function.
The four-page article “8080 Simulation with a 6502” (MICRO – The 6502 Journal, issue 16, September 1979) explains the motivation and design of the software in detail:
And here is the original commented source code with usage instructions:
Thanks a lot to Dann McCreary, who provided scans of his original work, as well as additional insights:
I wrote this by hand, pencil and paper assembly (BTW, did you ever read Carl Helmer’s article about pencil and paper in one of the very early issues of BYTE magazine? ;) and much of the simulator was written as I rode the bus to and from work… ;)
About the tools used to create this program:
Honestly, I don’t remember for certain… BUT… MORE THAN LIKELY, it is
a FAKE – i.e., I probably just text-edited a listing in “assembler
listing” format for the purpose of publishing the code and “looking
CONSEQUENTLY, be on the lookout for typographical (and thus operational)
errors that could be “in there” …
The all-upper-case makes me think I printed this stuff out on an old
drum printer that I resurrected from the American Surplus Computer
company in Boston back in the ’70s… And there’s yet another story! :)
The text editor may likely have been running on my Apple ][…. or maybe
“borrowed” from some company where I was working at the time?
Dann later ported the simulator to the Apple-][. The tape dump of the resulting product “Apple-80” can be found at brutaldeluxe.fr.