This message is from the T13 list server.
> > Seeing that C/D I/O = x01 CommandOut > > is the only way a host can distinguish between > > a DRQ expected to move command out > > from a DRQ expected to move command out. > The first time an ATAPI device > has status of BSY=0 and DRQ=1 > it is requesting the "command packet". Not necessarily. Yes the device "should be" requesting command out then. Maybe it is, maybe it isn't, the point of the Sff redundancy design here is to tell us. Suppose, for example, that the the x1F7 Command = xA0 Packet write occurred at a time when BSY:DRQ weren't both zero. The Ansi texts then very carefully tell us that we don't know what happens. So then it's very nice to have signals to hint at what might be going on. > The host NEVER needs > to look at IO and CD to determine this state. I think "needs" is a difficult word for two different people to interpret the same way. Seeing C/D I/O = x01 CommandOut tells the host that the device is signalling its state machine is where it should be. Pat LaVarre Subscribe/Unsubscribe instructions can be found at www.t13.org.
