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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
Programming Notes
Bit Definitions
AMD Athlon™ System Bus Dynamic Compensation (Dev0:F0:0x50)
Bit
Name
Function
31–24
Reserved
Reserved
23–20
Pval
P Transistor Strength Value
This field reflects the P transistor strength value that was automatically written to the
AMD Athlon™ processor system bus I/O pads by the auto-compensation circuit. In bypass
mode (bit 4=1) this field returns the values in the BYP_P field (bits [15:12]). The P values
are active Low.
19–16
NVal
N Transistor Strength Value
This field reflects the N transistor strength value that was automatically written to the
AMD Athlon processor system bus I/O pads by the auto-compensation circuit. In bypass
mode (bit 4=1) this field returns the values in the BYP_N field (bits [11:8]). The N values
are active High.
15–12
BYP_P
Bypass Values P Driver
Bypass strength values for the P driver. The P values are active Low. A value of 0 on bit 3
for instance signifies that (2^3 + 1) or 9 legs of the P driver are active.
11–8
BYP_N
Bypass Values N Driver
Bypass strength values for the N driver. The N values are active High. A value of 1 on bit 3,
for instance signifies that (2^3 + 1) or 9 legs of the N driver are active.
7–5
SlewCntl
Slew Rate Control
Slew rate control for AMD Athlon processor system bus.
000 = Slew rate 0 (slowest)
001 = Slew rate 1
010 = Slew rate 2
011 = Slew rate 3 (default)
100 = Slew rate 4
101= Slew rate 5
110 = Slew rate 6
111 = Slew rate 7 (fastest)
4
BYP
Bypass
Setting the bypass bit allows an external drive strength setting to be provided in the BYP_P
and BYP_N fields. Clearing this bit causes the drive strength to be provided by the
compensation circuit.
3-0
Reserved
Reserved