Ruud Baltissen wrote:
>
> Hallo allemaal,
>
> Daniele and I had an private discussion about building a 6502
> replacement for the above CPU's. I offered to draw a SCH. But I have no
> idea how the first two registers of the 8501 operate. Can anybody help on
> this, please?
The registers are just the same as in the 6510: $00 is the data direction
register and $01 is the data register. One bit is missing at the outside, but
if you use an 8 bit I/O port anyway, just don't connect the missing port bit
to the 7501 socket. you can see it in the pinout which port bit is missing.
Oh, maybe you'd better look at the schematic as well, I'm not sure the pinout
below is correct.
> I don't have the pinouts of the 8501 either. I can find out about these by
> having a peek at the SCHs at FUNET. But if somebody happened to have
> them at hand by coincidence, you would do me a big favour. Thanks.
There's a complete service manual for the Plus/4 on funet, and it contains
the processor pinout page. You could use that one. This is the page in
question:
http://www.funet.fi/pub/cbm/schematics/computers/plus4/manual/p4-07l.gif
Nicolas
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