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

From: Marko Mäkelä (
Date: 1999-08-03 12:48:43

Hello Frank,

> Bad thing with pinouts. Maybe two jumper would help something, but
> extreme care should be taken when... Better build two or three cables,
> than burn two or three computers.

True, but I think I'll try to build the universal cable.  I'll test it
first on the C64 and VIC-20, since my 8032-SK has an IEEE-488 like
connector for the user port.

> At least you can connect all commies at once to one PC and serve all
> at once.

If I had 3 bidirectional printer ports on my PC, yes.  Or 4, if I'll ever
get a similar interface for my C16.


The schematic diagram doesn't mention the resistor values.  The diagram at
<URL:> does.
I gather that the bigger resistors I use, the less likely it should be
that the interface chips get damaged.

> Would be very nice if near complete line of C='s would communicate
> with the same cable (with one PC :). The software's on C='s are
> different, but same (or one?) on the PC side.

With careful design, you could make the software auto-detect on which
computer it is running. :-)

The only unanswered question is: What is the DIAG pin on the PET user port
used for?  Can I safely program it as a '1' output and use it as a voltage
source for the 74HCT74 chip?


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