PLL Internal ref clock selection

Started by vvibin2003 June 25, 2003
Hi all,
Could any one explain me the criteria to select the value of
PLL Internal clock (REFCLOCK) which is used for the REFDIV
value calculation while setting up the PLL.

REFDIV = ((OSCCLOCK)/(REFCLOCK)) - 1



Hi,

I used use this method for calculating the SYNR and REFDV register values as follows

REFDV = OscClock (MHz) - 1;
SYNR = BusClock(MHz) -1;

Eg. If Oscillor is 8Mhz and System clock out of PLL is expected to be 40Mhz i.e. BusCock is 40/2 = 20Mhz

SYNR = 20 -1; SYNR= 19
REFDV = 8 -1; REFDV = 7

As per the formula the PLL out put Clock = 2 * OscClock* (SYNR+1) / (REFDV+1)

PLL Clock = 2 * 8 * (20) / (8) = 40Mhz
BusClock = 20Mhz

I hope this could be of any help to you.

Regards,
Mohan S S

@yahoo.com> wrote:
Hi all,
Could any one explain me the criteria to select the value of
PLL Internal clock (REFCLOCK) which is used for the REFDIV
value calculation while setting up the PLL.

REFDIV = ((OSCCLOCK)/(REFCLOCK)) - 1

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