I'm using GPBUS to read/write a number of 8-bit ports. My problem is
reading using GPBUS read cycle doesn't seem to work. Writing a port
works flawlessly, but with a read cycle, GPBUS pins 0-7 remain as
outputs and that drives my card's outputs to the programmed data value
for those bits, which I'm not sure what should be. 7400's info doesn't
specify if data bits should be 0xff or 0x00 in order to accomplish a
read. To make things worse, I don't have a LVCMOS bus transceiver, so
I'm coupling 5V to 3.3V with series resistors and clamp diodes. I'm
suspecting my series resistors could be too high to drive GPBUS bits
as outputs, but don't know where to look for that info. Has anybody
constructed something like this? So far, my solution has been "manual"
read cycle ( generating read cycle's stages one by one with individual
instructions ) which works OK, but I'm still curious about the correct
solution ( automatic GPBUS read cycle ). Thanks in advance
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