Playing with ATN inhibit at the 6522 IC. If I disconnect ATN input to 6522 and ATNACK from 6522, and hook the two pins from the socket together, (thereby tying both pins of the 74'86 to the same value), I can create a device not present condition. The interesting behavior occurs if I have previously used the disk drive. If I perform this mod immediately after reset, the circuit works as expected. If I perform it after a disk access, the computer locks up waiting for a response. I have verified it's not the computer, but the drive. I put a LA on the signals. After reset, with my mod,, a bus request causes the ATN and ATNACK lines to cycle for a while and then go low. After a disk access, then my mod, a bus request causes ATN and ACK to cycle for a bit and then go high. I'm struggling to understand the differences. I assume the code is doing something slightly different at IDLE after a disk access from what happens after RESET. Jim -- Jim Brain firstname.lastname@example.org www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2013-10-11 03:00:04
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