AMD-761 Datasheet, PDF (104/264 Pages) Advanced Micro Devices – AMD-761-TM System Controller Software/BIOS Design Guide

Preliminary Information
AMD-761™ System Controller Software/BIOS Design Guide
24081D—February 2002
Bit Definitions
Bit Name
31–28 BYP_PDrvXfer
27–24 BYP_NDrvXfer
23 BYPXfer
22–20 Reserved
19–18 PSlewXfer
17–16 NSlewXfer
15–12 BYP_PDrvStrb
11–8 BYP_NDrvStrb
7 BYPStrb
6–4 Reserved
AGP Compensation Bypass (Dev0:F0:0xB8)
Function
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.
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.
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.
Reserved
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)
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)
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.
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.
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.
Reserved
92
AMD-761™ System Controller Programmer’s Interface
Chapter 2