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Signal Descriptions
Interface Control Pins
4-6
SYM53C825A/825AE Data Manual
Table 4-4: Interface Control Pins
Symbol
Pin No.
Type
Description
FRAME/
16
S/T /S
Cycle Frame is driven by the current master to indicate the begin-
ning and duration of an access. FRAME/ is asserted to indicate a
bus transaction is beginning. While FRAME/ is asserted, data trans-
fers continue. When FRAME/ is deasserted, the transaction is in
the final data phase or the bus is idle.
Target Ready indicates the target agent’s (selected device’s) ability
to complete the current data phase of the transaction. T RDY/ is
used with IRDY/. A data phase is completed on any clock when
both T RDY/ and IRDY/ are sampled asserted. During a read,
T RDY/ indicates that valid data is present on AD(31-0). During a
write, it indicates the target is prepared to accept data. Wait cycles
are inserted until both IRDY/ and T RDY/ are asserted together.
Initiator Ready indicates the initiating agent’s (bus master’s) ability
to complete the current data phase of the transaction. T his signal is
used with T RDY/. A data phase is completed on any clock when
both IRDY/ and T RDY/ are sampled asserted. During a write,
IRDY/ indicates that valid data is present on AD(31-0). During a
read, it indicates the master is prepared to accept data. Wait cycles
are inserted until both IRDY/ and T RDY/ are asserted together.
Stop indicates that the selected target is requesting the master to
stop the current transaction.
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.
Initialization Device Select is used as a chip select in place of the
upper 24 address lines during configuration read and write transac-
tions.
T RDY/
19
S/T /S
IRDY/
17
S/T /S
ST OP/
22
S/T /S
DEVSEL/
20
S/T /S
IDSEL
2
I
Table 4-5: Arbitration Pins
Symbol
Pin No.
Type
Description
REQ/
148
O
Request indicates to the arbiter that this agent desires use of the
PCI bus. T his is a point-to-point signal. Every master has its own
REQ/.
Grant indicates to the agent that access to the PCI bus has been
granted. T his is a point-to-point signal. Every master has its own
GNT /.
GNT /
147
I