Bug in Genxt

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Ruud
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Joined: Wed 28 Oct, 2015 7:20 am

Bug in Genxt

Post by Ruud »

I mentioned in an earlier tread, the one about the Landmark diagnostic ROM, that I was developing a diagnostic ROM myself. The IBM-PC has two dip switch blocks, SW1 and SW2. SW1 is read by reading port A of the 8255 after bit 7 of port B has been set to 1. SW2 is read by reading the bits 4..7 of port C. The only dip switch block of the IBM-XT and compatibles is read in the same way.
Because in a XT the original hardware for reading SW1 doesn't exist any more and the 74LS322, used for outputting the data of the keyboard, has been tri-stated, I expect port A to read FF. Instead I read 00 using GenXT. I suspect that this will happen as well when using IBMXT. FYI, I read FF on a real XT.

I hope somebody can repair this. Many thanks in advance!

Kind regards, Ruud Baltissen
Groetjes / kind regards, Ruud Baltissen
http://www.Baltissen.org
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