6 Apr
2010
6 Apr
'10
2:25 p.m.
Tony Duell wrote:
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.
... 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?