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| From: Richard Atkinson
Date: 2001-09-25
Subject: Re: Reading the cassette sense line?
|
On Tue, 25 Sep 2001, Marko Mäkelä wrote:
> I could otherwise use the cassette sense line bidirectionally, but the
> line is unidirectional in the plus/4. In all other Commodores, including
> the PET, the P500 and the CBM II series, the line is bidirectional.
>
> Since the cassette sense line is wired in a weird way in the plus/4, I'd
> like to ask the plus/4 experts' advice: how can the state of the line
> determined by the processor (sample machine code, please)?
On the plus/4, CST SENSE is wired to bit 2 of the user port 6529 single port interface (also pin 4 of the user port). You can read it and write to it in the normal 6529 manner.
The C16 and 116 use a tristate buffer to drive the state of CST SENSE onto the data bus at bit 2 whenever the $FD1x address space is accessed, but note this even happens when writing to that address, so contention of D2
may occur. I don't think it's possible to set the line low with the computer hardware.
Richard
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