ICS94201 Datasheet, PDF (8/18 Pages) Integrated Circuit Systems – Programmable System Frequency Generator for PII/III™

ICS94201
Byte 13: ICS Reserved Register
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PWD
Description
0 (Reserved)
0 (Reserved)
0 (Reserved)
W0 timer base select
0 0=580ms
1=2ms
0 (Reserved)
0 (Reserved)
0 (Reserved)
0 (Reserved)
Note: DON'T write a '1' into this register, it will
cause malfunction.
Byte 14: VCO Frequency Control Register
Bit PWD
Description
Bit 7 X VCO Divider Bit0
Bit 6 X REF Divider Bit6
Bit 5 X REF Divider Bit5
Bit 4 X REF Divider Bit4
Bit 3 X REF Divider Bit3
Bit 2 X REF Divider Bit2
Bit 1 X REF Divider Bit1
Bit 0 X REF Divider Bit0
Note: The decimal representation of these 7 bits (Byte 14
[6:0]) + 2 is equal to the REF divider value .
Byte 15: VCO Frequency Control Register
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PWD
Description
X VCO Divider Bit8
X VCO Divider Bit7
X VCO Divider Bit6
X VCO Divider Bit5
X VCO Divider Bit4
X VCO Divider Bit3
X VCO Divider Bit2
X VCO Divider Bit1
Note: The decimal representation of these 9 bits (Byte 15 bit
[7:0] & Byte 14 bit [7] ) + 8 is equal to the VCO divider value.
For example if VCO divider value of 36 is desired, user need
to program 36 - 8 = 28, namely, 0, 00011100 into byte 15 bit
& byte 14 bit 7.
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
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 desired 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 6 for readback of 25 bytes (byte 0-24).
3. Read back byte 16-24 and copy values in these registers.
4. Re-initialize the write sequence.
5. Write a '1' to byte 8 bit 7 indicating you want to use byte 14 and 15 to control the VCO frequency.
6. Write to byte 14 & 15 with the desired VCO & REF divider values.
7. Write to byte 16 to 24 with the values you copy from step 3. This maintains the output divider mux controls the same gear ratio.
8. The above procedure is only needed when changing the VCO for the 1st pass. If VCO frequency needs to be changed again,
user only needs to write to byte 14 and 15 unless the system is to reboot.
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