Date: 2001-04-24 14:33:27

On Tue, 24 Apr 2001 wrote:

> >what was this person up to?  Is such a hack even POSSIBLE in a >710/720?
> Can
> >Commodore Serial disk drives be driven from the lines in the >>datasette
> >port?!?!
> To drive the IEC serial bus Open Collector chips are normally needed so that
> there is no conflict between various devices working the bus. If there is no
> 7406 (or similar) chip in the circuit, chances are it is a naive attempt at
> the modification, and potentially risky. The O/C function allows devices to
> pull the signal "low" and to "let go". Without the "let go" function, you
> get "pull high" which can lead to a bus contention.

Unless a clever programmer sets the outputs to '0' and uses the DDR to
toggle the lines ;)  THis would give you your pull and let go feature.  The
only thing you need beyond this is a pull-up resistor on each line.

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