Hallo Jim, So far I didn't have time to have a good look at it. > If I disconnect ATN input to 6522 and ATNACK from 6522, ... Looking at the SCH the ATN goes to two inputs, PB7 and CA1. > (thereby tying both pins of the 74'86 to the same value), Just to be sure, you connect pin 1 and pin2 of UD3 together. If both pins have the same value all the time, the output is always (L). The output goes to pin 11 of the 06 OC inverter UB1 and therefore its output will always be tri-stated. > I can create a device not present condition. I'm not familiar with the communication protocol of IEC drives. IEEE drives pull NDAC (L) the moment ATN becomes (L). The very first moment this is done by hardware but it is taken over by software. This is the first check for the computer that there is a device present at all. Looking at the SCH I think the data line has this function. The first byte to be sent by the computer, while ATN is still (L), should be the device number. If it is not the number of the device, it will release NDAC. No NDAC present at all after sending the device number means there isn't any device available with this number. So IMHO the data line should be kept (L) to tell that the device is present. The only thing that can make the C64 hang is that the data line is made (L) at a certain point AFTER your first try. The only one who can do that is the drive. If both inputs had been disconnected, I cannot see any reason at all for the 1541 to do such a thing. But you mentioning disconnecting only one input, my interpretation, I can imagine that the 1541, acting on CA1, activates the data line in software after the moment the C64 has decided that there is no drive present. At the next access, the data line is still (L) so the C64 kindly waits until it is released. OK, a bit a wild guess but I hope this helps :) Met vriendelijke groet / with kind regards, Ruud Baltissen De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken. Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij overgebrachte virussen. APG Algemene Pensioen Groep NV is gevestigd te Heerlen en is ingeschreven in het handelsregister van de Kamer van Koophandel Limburg onder nummer 14099617 The information contained in this e-mail is confidential and may be privileged. It may be read, copied and used only by the intended recipient. If you have received it in error, please contact the sender immediately by return e-mail; please delete in this case the e-mail and do not disclose its contents to any person. We don't accept liability for any errors, omissions, delays of receipt or viruses in the contents of this message which arise as a result of e-mail transmission. APG Algemene Pensioen Groep NV is registered in the trade register of the Chamber of Commerce Limburg, The Netherlands, registration number: 14099617 Message was sent through the cbm-hackers mailing listReceived on 2013-10-12 08:00:04
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