Posted By
MCes
on 2019-04-04
12:39:01
 |  Plus4 / C16 CPU replacement chip
I'm working around at a project of mine: create a reliable substitute for 7501-8501.
The alfa version (experimental board) is working....
Which tests I can do?
https://postimg.cc/gallery/ewfx83uw/
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Posted By
SVS
on 2019-04-04
15:00:39
 | Re: Plus4 / C16 CPU replacement chip
Hi,
very interesting work! 
In order to test it you could try Test suite v2
Let we know all the future progress 
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Posted By
MCes
on 2019-04-04
15:22:08
| Re: Plus4 / C16 CPU replacement chip
It's based on very fast C-Mos version of 6502 CPU (fast timings are requested) so the original illegal opcode are not supported: it's the only limit that I know at this project!
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Posted By
MCes
on 2019-04-04
15:23:25
| Re: Plus4 / C16 CPU replacement chip
It's work with original kernal, cassette and 1541 (on serial cable)...
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Posted By
gerliczer
on 2019-04-05
15:13:22
| Re: Plus4 / C16 CPU replacement chip
Can that 65C02 (or whatever) be replaced with an original NMOS 6502?
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Posted By
MCes
on 2019-04-07
11:30:14
| Re: Plus4 / C16 CPU replacement chip
8501 is a 6502 that can:
1) run @ 2 MHz
2) hardware timings referred to entering clk line (CPU is slave) and not referred to output CLK line (CPU master: a normal 6502 activity)
3) R/W line is "sampled & holded" by MUX signal on specific timings (6502 hasn't "S&H" circuit inside...)
4) bus pins can become tre-state (as MOS6510)
5) a bidirectional parallel port of 7bit is provided
I seen a 6510 for replacing a 8501, but it match only the point n°4.....
A 6502 can be hardware upgraded if it match 8501 on point n°1,2.
Note that point n°2 imply that probabilly the 6502 has to be @3MHz or more (a master CPU has to become a slave CPU)
points n°3,4,5 have to be performed by extra hardware....
remember that "not c-mos version" of 6502 is discontinued: if you buy a new Rockwell R6502B ("B"=3MHz) 90% it's a fake refurbished from every kind (and speed...) of 6502, may be a C-Mos version!
Making this project with a N-Mos 6502 can be done, but with more hardware and with serious problem of finding the right 6502 chips...
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