Target abort -computer architecture:
Usually, a target holds DEVSEL# asserted through the final data phase. However, if a target desserts DEVSEL# before disconnecting without data (asserting STOP#), it indicates a target abort, which is a fatal error condition. The initiator may not retry, and usually treats it as a bus error. Note that a target may not dessert DEVSEL# as waiting with TRDY# or STOP# low; it have to do this at the starting of a data phase. After observing STOP#, the initiator will terminate the transaction at the next legal chance, but if it has already signaled its wish to continue a burst (by asserting IRDY# without deserting FRAME#), it is not allowed to dessert FRAME# till the following data phase. A target that requests a burst end (asserting STOP#) can have to wait through another data phase (holding STOP# asserted without TRDY#) before the transaction can stop.
Data transfer signals on the PCI bus.
Read operation on the PCI Bus
Read operation showing the role of the TRDY #, IRDY #