LSI 53C875A Interface Control Signals, Initialization Device Select is used as a chip select

3.3.3 Interface Control Signals

		Table 3.4 describes the Interface Control signals.
Table 3.4	Interface Control Signals
Name	PQFP	BGA	Type	Strength	Description
FRAME/	16	F2	S/T/S	8 mA PCI	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 deasserted, either the transaction is
					in the final data phase or the bus is idle.
TRDY/	19	G3	S/T/S	8 mA PCI	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/	17	F1	S/T/S	8 mA PCI	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/	22	G4	S/T/S	8 mA PCI	Stop indicates that the selected target is requesting
					the master to stop the current transaction.
DEVSEL/	20	G2	S/T/S	8 mA PCI	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	2	B1	I	N/A	Initialization Device Select is used as a chip select in
					place of the upper 24 address lines during
					configuration read and write transactions.

3-6 Signal Descriptions