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.

 

 

 

 

PCI Bus Interface Signals

4-7

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LSI 53C810A technical manual Interface Control Signals