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AMD-761™ System Controller Programmer’s Interface
Chapter 2
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Preliminary Information
Bit Definitions
AGP Compensation Bypass (Dev0:F0:0xB8)
Bit
Name
Function
31–28
BYP_PDrvXfer
P Drive Strength Control
This field is used to directly program the P transistor drive strength on all AGP pins except
the data strobes. A value of 0000 is the weakest, 1111 is the strongest. This value is written
to the I/O pads only when BYPXfer (bit 23) is set.
27–24
BYP_NDrvXfer
N Drive Strength Control
This field is used to directly program the N transistor drive strength on all AGP signals
except the data strobes. A value of 0000 is the weakest, 1111 is the strongest. This value is
written to the I/O pads only when BYPXfer (bit 23) is set.
23
BYPXfer
Bypass Enable
This bit must be set to bypass the auto-compensation circuit for direct control of all AGP
pads except the strobe pins. When this bit is set, the values programmed in the drive
strength fields are written directly to the pads.
22–20
Reserved
Reserved
19–18
PSlewXfer
Slew Rate Control
This field is used to directly program the rise time in all AGP signals except the data
strobes. This field is not affected by the BYPXfer bit.
00 = Slew rate 0 (slowest)
01 = Slew rate 1
10 = Slew rate 2
11 = Slew rate 3 (fastest)
17–16
NSlewXfer
Slew Rate Control
This field is used to directly program the fall time in all AGP signals except the data strobes.
This field is not affected by the BYPXfer bit.
00 = Slew rate 0 (slowest)
01 = Slew rate 1
10 = Slew rate 2
11 = Slew rate 3 (fastest)
15–12
BYP_PDrvStrb
P Drive Strength Control
This field is used to directly program the P transistor drive strength on the AGP data
strobes (AD_STB[1:0], AD_STB[1:0]#). A value of 0000 is the weakest, 1111 is the
strongest. This value is written to the I/O pads only when BYPStrb (bit 7) is set.
11–8
BYP_NDrvStrb
N Drive Strength Control
This field is used to directly program the N transistor drive strength on all AGP data
strobes (AD_STB[1:0], AD_STB[1:0]#). A value of 0000 is the weakest, 1111 is the
strongest. This value is written to the I/O pads only when BYPStrb (bit 7) is set.
7
BYPStrb
Bypass Enable
This bit must be set to bypass the auto-compensation circuit for direct control of all AGP
strobe pins (AD_STB[1:0], AD_STB[1:0]#). When this bit is set, the values programmed in
the drive strength fields are written directly to the pads.
6–4
Reserved
Reserved