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Old 02 March 2017, 14:51   #71
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Join Date: Mar 2012
Location: Norfolk, UK
Posts: 577
Originally Posted by witchmaster View Post
it's not safe to do it this way because of the input/output on the same pin issue (this could do damage to the microprocessor or the Amiga).
It's always safe to short the pin to ground - since the pin on the Amiga is designed to have a mouse button attached to it - the only danger is if the Amiga's driving the pin low while the uC is driving it high. You can avoid that by using "input with weak pull-up enabled" instead of "output logic high". But using the tristate IC is a much better idea.

Also I'm only testing on my A500 at the moment, it's working on that but I guess the problem with logic zero can show up on other motherboards.
Yes, I never saw this issue on an A500 or my A4000/030 when I had that, but it apparently affected some A1200s and I think A600s too. I don't know about the CD32 (The same problem shows up with some PC mouse adapters whe then right mouse button doesn't work.)

Ok, good to know! I guess the timing for when sending the clock signals and reading the data can vary in the code.
Yes, basically the code polls a CIA register multiple times to create a fixed delay, allowing the shift register to do its thing. Some games poll the register fewer times, cutting the timing to the absolute minimum.
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