PET 4032 keyboard scanning problem / was Re:Anyone have an image
hilpert at cs.ubc.ca
Tue Apr 6 16:25:07 CDT 2010
Tony Duell wrote:
> > ... pulled out my notes from 2004: I had scoped the lines from the 6520 to the
> > '145 1-of-10 decoder, the observed 4-bit scan sequence driving the 145 is
> > 09ABCDEF0 rather than 0->9, so only 2 lines instead of 10 on one side of the
> > keyboard matrix are being scanned.
> Hat it been 89ABCDEF8989ABCDEF... I would have guessed that the D input
> was stuck highm possibly due to a defect in the PIA or a bad connection
> (the PIA is socketed IIRC). Are you sure it's not this sequence?
I had scoped all 4 lines and determined the count sequence from the time
relationship of the pulses on those lines. While it is possible that on one of
those 4 lines I was somehow blind to the distinction between a pulse and a
constant high, it is highly unlikely. In this instance, the unlikely did not occur.
I also scoped the 10 active-low outputs from the 145 with a pull-up resistor
added because the outputs are OC and don't show their state well without. Only
2 go low (0 & 9).
The 6520 PIA is soldered in.
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