Datasheet

Signal Description

Datasheet 33

2.3 AGP Interface Signals

Unless otherwise specified, the voltage level for all signals in this interface is 1.5 volts.

2.3.1 AGP Addressing Signals

Table 5. AGP Addressing Signal Descriptions

Signal Name Type Description

GPIPE# I

AGP

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

full width address is to be enqueued on by the target using the AD bus.

One address is placed in the AGP request queue on each rising clock edge

while PIPE# is asserted. When PIPE# is deasserted no new requests are

queued across the AD bus.

During SBA Operation: This signal is not used if SBA (Side Band

Addressing) is selected.

During FRAME# Operation: This signal is not used during AGP FRAME#

operation.

PIPE# is a sustained tri-state signal from masters (graphics controller), and

is an input to the GMCH/MCH.

GSBA[7:0] I

AGP

Side-band Address: These signals are used by the AGP master (graphics

controller) to pass address and command to the GMCH/MCH. The SBA

bus and AD bus operate independently. That is, transactions can proceed

on the SBA bus and the AD bus simultaneously.

During PIPE# Operation: These signals are not used during PIPE#

operation.

During FRAME# Operation: These signals are not used during AGP

FRAME# operation.

NOTE: When sideband addressing is disabled, these signals are isolated

(no external/internal pull-ups are required).

The AGP interface contains two mechanisms to queue requests by the AGP master. Note that the

master can only use one mechanism. The master may not switch methods without a full reset of

the system. When PIPE# is used to queue addresses the master is not allowed to queue addresses

using the SBA bus. For example, during configuration time, if the master indicates that it can use

either mechanism, the configuration software will indicate which mechanism the master will use.

Once this choice has been made, the master will continue 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.