Hello! Ruud@Baltissen.org wrote: > If a device is present, send device number. All devices not having > this number, will release NDAC and NRFD. So if both NRFD and NDAC > become (H), the wanted device is not present. Only after the device > has shown its present, you start with TALK, LISTEN or what ever. No you don't. It's a common misconception I also shared before I started implementing this stuff. In fact there are even two important misconceptions here: * The NDAC signal is _not_ used to signal whether the device is preent or not. It is simply a signal to _acknowledge_ that a device has seen the byte placed on the bus. And the important thig is that _all_ devices are required to acknowledge all bytes placed on the bus. So this signal does not indicate whether the device understood the data or not, only that it has seen it. So if you have a device on #8 on the bus and you send LISTEN to device #9, the device #8 is still required by the standard to use NDAC whe seeing this command. * There is no anything like "send device number" on the bus by itself. By placing the device number on the bus, you are _already_ sending TALK or LISTEN command, because that's exactly what these commands are - a device number is placed on the bus with ATN signal asserted. In fact, all this information comes from the document posted on your own site ;-) http://www.baltissen.org/newhtm/ieee.htm Se also this document where this handshaking operation is nicely explained: http://www.raunvis.hi.is/~rol/Vefur/%E9r%20Instrupedia/CGPTUTO.PDF There is no provision in the IEEE protocol itself for detecting the presence or non-presence of a device on the bus. You can only learn if the device is present or not using some higher level protocol. Just like I am doing in my code (opening a file and waiting for a response from the drive). Regards, Michau. Message was sent through the cbm-hackers mailing listReceived on 2014-11-09 15:00:03
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