9

ICS94236

0451A

—01/10/03

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

Note:

1. User needs to ensure step 3 & 7 is carried out. Systems with wrong spread percentage and/or group to group skew

relation programmed into bytes 13-16 could be unstable. Step 3 & 7 assure the correct spread and skew relationship.

2. If VCO, REF divider values or phase detector stability are out of range, the device may fail to function correctly.

3. Follow min and max VCO frequency range provided. Internal PLL could be unstable if VCO frequency is too fast or

too slow. Use 14.31818MHz x VCO/REF divider values to calculate the VCO frequency (MHz).

4. ICS recommends users, to utilize the software utility provided by ICS Application Engineering to program the VCO

frequency.

5. Spread percent needs to be calculated based on VCO frequency, spread modulation frequency and spreadamount

desired. See Application note for software support.

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.

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.

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Byte 19: Reserved Register

are unused registers writing to these registers

will not affect device performance or

functinality.

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Byte 20: Reserved Register