Date: 2001-04-24 09:31:23

>what was this person up to?  Is such a hack even POSSIBLE in a >710/720?
>Commodore Serial disk drives be driven from the lines in the >>datasette

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.

People have use the tape port on the C64/C128 to interact with PC keyboards,
these also use O/C logic. The implementations are essentially "listener
only", which might work, but a drive needs to be "talker" and "listener".

>From memory the cassette port has no O/C circuit, but one line has a pull up
resistor (the sense), another a transistor driver  circuit(motor), and the
read/write lines are straight through from the 6526/CPU, respectively.

I imagine a professional cassette port adaptor would probably include O/C
driver chip.

- Nick


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