I have swapped the 6520s over and I get the same result - bits 7 and 0 fail.
Colin.
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Originally Posted by SiriusHardware
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After the first POKE, all connections are 0.05V. After the second POKE, all connections are c. 3.25V with the exception of D which is c. 4.3V
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Looks like the outputs are driving OK but that different voltage on the 'D' line (= bit 7) is indicative that something is not right there - most likely a fault on the buffer input which is connected to that input / output line.
Try swapping the 6520s over temporarily and re-run your port test program. If the fault report does not change when you do that, that rules out the 6520. |