Signal Description

R

2.4AGP Interface Signals

2.4.1AGP Addressing Signals

Signal Name

Type

Description

 

 

 

PIPE#

I

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

 

AGP

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: Not Used.

 

 

During FRAME# Operation: Not Used.

 

 

PIPE# is a sustained three-state signal from masters (graphics

 

 

controller), and is an MCH input.

 

 

Note: Initial AGP designs may not use PIPE# (i.e., PCI only 66 MHz).

 

 

Therefore, an 8 kpull-up resistor connected to this pin is

 

 

required on the motherboard.

 

 

 

SBA[7:0]

I

Sideband Address: These signals are used by the AGP master

 

AGP

(graphics controller) to place addresses into the AGP request queue.

 

 

The SBA bus and AD bus operate independently. That is, a transaction

 

 

can proceed on the SBA bus and the AD bus simultaneously.

 

 

During PIPE# Operation: Not Used.

 

 

During FRAME# Operation: Not Used.

 

 

Note: When sideband addressing is disabled, these signals are

 

 

isolated (no external/internal pull-up resistors are required).

 

 

 

NOTE: The above table 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.

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Intel® 82845 MCH for SDR Datasheet

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Intel 845 AGP Interface Signals, AGP Addressing Signals, During SBA Operation Not Used, During FRAME# Operation Not Used