I bow to the knowledge of those who understand DOS better than I, but I am confused about the operation of the ATNACK circuit in the 1541. Now that I finally have a good PC-based logic analyzer, I submit two traces for perusal: load"$",9 http://s15.postimage.org/pym7z9i23/with_ACK.png If I then remove pin 10 of UB1 (the '06 that outputs the result of the ACK circuit onto the DATA line), I get this trace http://s15.postimage.org/ar68ewq7b/without_ACK.png Legend: All signals are tapped at the 6522 except DATA_ACK which is tapped off of UB1:pin 11 (high there means a low on the DATA line) What I am seeing: * ATN_IN goes high (at the 6522) * it takes 444uS to bring DATA_OUT hi (which would pull DATA low) * command data sent * ATN_IN goes LOW * data is sent * At 7.4ms, ATN_IN goes high again * ATNACK is already low, so DATA_ACK goes high * DATA_OUT is already hi, so all is well * Than, at 9.443mS, ATN goes high again * DATA never goes high, ever * ATN_IN cycles a few times (zoomFLoppy), trying to get a response. I don't understand why the DOS never notices ATN at 9.443ms I am looking through the DOS routines, but it's slow going for me. Maybe someone with a bit more DOS knowledge can shed some light on it. I can create more traces if needed. Jim -- Jim Brain email@example.com www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2012-03-30 01:00:05
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