845GL datasheet(29/193 Pages) INTEL

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Intel® 82845G/82845GL/82845GV GMCH Datasheet

Signal Description

2.4

AGP Interface Signals

2.4.1

AGP Addressing Signals

Note: The above table contains two mechanisms to queue requests by the AGP master. Note that the

master can only use one mechanism. When PIPE# is used to queue addresses, the master is not

allowed to queue addresses using the sideband (SB) bus. During configuration time, if the master

indicates that it can use either mechanism, the configuration software indicates which mechanism

the master will use. Once this choice has been made, the master continues to use the mechanism

selected until the master is reset (and reprogrammed) to use the other mode. This change of modes

is not a dynamic mechanism but rather a static decision when the device is first being configured

after reset.

2.4.2

AGP Flow Control Signals

Signal Name

Type

Description

GPIPE#

AGP

Pipelined Read: This signal is asserted by the current master to indicate a full

width address is to be queued by the target. The master queues one request each

rising clock edge while GPIPE# is asserted. When GPIPE# is deasserted, no new

requests are queued across the GAD bus.

GPIPE# is a sustained tri-state signal from the master (graphics controller) and is

an input to the GMCH.

GSBA[7:0]

AGP

Sideband Address: This bus provides an additional bus to pass addresses and

commands to the GMCH from the AGP master.

Signal Name

Type

Description

GRBF#

AGP

Read Buffer Full: This signal indicates if the master is ready to accept previously

requested low priority read data. When GRBF# is asserted, the GMCH is not

allowed to return low priority read data to the AGP master. GRBF# is only

sampled at the beginning of a cycle.

If the AGP master is always ready to accept return read data, it is not required to

implement this signal.

GWBF#

AGP

Write Buffer Full: This signal indicates if the master is ready to accept fast write

data from the GMCH. When GWBF# is asserted, the GMCH is not allowed to

drive fast write data to the AGP master. GWBF# is only sampled at the beginning

of a cycle.

If the AGP master is always ready to accept fast write data, it is not required to

implement this signal.

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