8

ICS94201

0428B - 11/28/05

Byte 13: ICS Reserved Register

Byte 15: VCO Frequency Control Register

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.

Note: DON'T write a '1' into this register, it will

cause malfunction.

Byte 14: VCO Frequency Control Register

Note: The decimal representation of these 7 bits (Byte 14

[6:0]) + 2 is equal to the REF divider value .

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 (19H) 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.

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)

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