ICS951901 Datasheet, PDF (7/19 Pages) Integrated Circuit Systems – Programmable Frequency Generator & Integrated Buffers for Pentium III Processor

ICS951901
Byte 17: Output Rise/Fall Time Select Register
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PWD
1
0
1
0
1
0
Description
PCI (3:0) Slew Rate Control
PCI_F Slew Rate Control
CPUCLK2 Slew Rate Control
0 CPUCLK1 Slew rate Control
Byte 18: Output Rise/Fall Time Select Register
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PWD
1
0
1
0
1
0
1
0
Description
SDRAM12: Slew Rate Control
AGPCLK1: Slew Rate Control
AGPCLK0: Slew Rate Control
PCICLK4: Slew Rate Control
Byte 19: Output Rise/Fall Time Select Register
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PWD
1
0
1
0
1
0
1
0
Description
48MHz: Slew Rate Control
24_48MHz: Slew Rate Control
REF1: Slew Rate Control
REF0: Slew Rate Control
SDRAM (11:0): Slew Rate Control
VCO Programming Constrains
VCO Frequency ...................... 150MHz to 500MHz
VCO Divider Range ................ 8 to 519
REF Divider Range ................. 2 to 129
Phase Detector Stability .......... 0.3536 to 1.4142
Useful Formula
VCO Frequency = 14.31818 x VCO/REF divider value
Phase Detector Stabiliy = 14.038 x (VCO divider value)^-0.5
Byte 20: Output Rise/Fall Time Select Register
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PWD
0 Reserved
0 Reserved
0 Reserved
0 Reserved
0 Reserved
0 Reserved
Description
0 CPUCLK0 Slew Rate Control
To program the VCO frequency for over-clocking.
0. Before trying to program our clock manually, consider using ICS provided software utilities for easy
programming.
1. Select the frequency you want to over-clock from with the desire gear ratio (i.e. CPU:SDRAM:3V66:PCI ratio) by
writing to byte 0, or using initial hardware power up frequency.
2. Write 0001, 1001 (19_H) to byte 8 for readback of 21 bytes (byte 0-20).
3. Read back byte 11-20 and copy values in these registers.
4. Re-initialize the write sequence.
5. Write a '1' to byte 9 bit 7 and write to byte 11 & 12 with the desired VCO & REF divider values.
6. Write to byte 13 to 20 with the values you copy from step 3. This maintains the output spread, skew and slew
rate.
7. The above procedure is only needed when changing the VCO for the 1st pass. If VCO frequency needed to be
changed again, user only needs to write to byte 11 and 12 unless the system is to reboot.
0670B—07/15/04
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