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PCI Bus Interface Signals 4-7
4.1.3 Interface Control Signals
Table 4.4 describes the Interface Control Signals group.
Table 4.4 Interface Control Signals
Name Pin No. Type Description
FRAME/ 11 S/T/S Cycle Frame is driven by the current master to indicate the beginning
and duration of an access. FRAME/ is asserted to indicate that a bus
transaction is beginning. While FRAME/ is asserted, data transfers
continue. While FRAME/ is deasserted, either the transaction is in the
final data phase or the bus is idle.
TRDY/ 14 S/T/S Target Ready indicates the target agent’s (selected device’s) ability
to complete the current data phase of the transaction. TRDY/ is used
with IRDY/. A data phase is completed on any clock when used with
IRDY/. A data phase is completed on any clock when both TRDY/ and
IRDY/ are sampled asserted. During a read, TRDY/ indicates that
valid data is present on AD[31:0]. During a write, it indicates that the
target is prepared to accept data. Wait cycles are inserted until both
IRDY/ and TRDY/ are asserted together.
IRDY/ 12 S/T/S Initiator Ready indicates the initiating agent’s (bus master’s) ability to
complete the current data phase of the transaction. IRDY/ is used
with TRDY/. A data phase is completed on any clock when both IRDY/
and TRDY/ are sampled asserted. During a write, IRDY/ indicates that
valid data is present on AD[31:0]. During a read, it indicates that the
master is prepared to accept data. Wait cycles are inserted until both
IRDY/ and TRDY/ are asserted together.
STOP/ 17 S/T/S Stop indicates that the selected target is requesting the master to
stop the current transaction.
DEVSEL/ 15 S/T/S Device Select indicates that the driving device has decoded its
address as the target of the current access. As an input, it indicates
to a master whether any device on the bus has been selected.
IDSEL 97 I Initialization Device Select is used as a chip select in place of the
upper 24 address lines during configuration read and write
transactions.