Re: A parallel interface for PET, VIC-20 and C64/C128

From: Marko Mäkelä (
Date: 1999-08-04 12:15:56

On Wed, 4 Aug 1999, Frank Kontros wrote:

> Anyway welcomned. Would you also interested in diskcopier prg for
> 1541->C64/C128/C65->PC (I just remembered that sometime ago I promised
> you send it).

Yes, of course I'm interested.  Perhaps then I will finally have a disk
copier that does its job in a reasonable amount of time (such as 1-2

> Marko> The schematic diagram doesn't mention the resistor values.
> Because they're are removed from schematic. They makes much mess
> than protect.

What about using fuses on each line? :-)

> Marko> With careful design, you could make the software auto-detect on which
> Marko> computer it is running. :-)
> Hmmm. How? Eg. KERNAL patch. Make all routines in 3 or 4 versions?

Make the default load address $0401, because that is the start address of
PET BASIC programs.  Then assume that the load address is $xx01 and invoke
the machine language with a line of BASIC code:
 1999 SYS256*PEEK(44)+something
Then the machine language will detect its running address
(LDA#$60:STA$0100:JSR$0100:TSX:LDA$01xx,X and so on) and patch the
routines and/or the routine that installs them accordingly.  The hardware
can be detected by looking at some ROM locations or at some locations that
ought to have I/O chips.

> Don't know. Maybe you can source 74HCT74 from LPT port of PC too.

I wouldn't count on that.  There are so many different types of PC
parallel ports around.  It is true that this cable is only designed for
PS/2-style parallel ports, but having seen how many differences there are
between the "traditional" PC parallel port designs, I would rather do the
kludges on the Commodore side.

So, is it safe to use the DIAG input as a power source, and does it have
other functions than activating the diagnostic routines?


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