# PLL Internal ref clock selection

Started by 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 -------------------- ---------------------------------