Johan Sandgren

PLL never locks - HC908AP64 - clueless...help ?

Discussion created by Johan Sandgren on Mar 21, 2011
Latest reply on Mar 22, 2011 by bigmac
Hi,
I have a problem with a PLL not locking, never finishing and I cannot find the problem. I need your help please.
I'm using a MC908AP64 (HC08) with an external crystal 32768Hz according to suggested build from cpu-pdf-manual.
The board is custom built. We have designed OSC1 and OSC2 connected to R1 10M parallell, and X1 32768Hz, and 2 x C1 (12p) to ground, like the design example in the manual.
I attached the schematics for you to see.
I created a CPU setup with initialization tool... and have attached the project as well.
Noticed that it never seems to lock. 
I designed so that after this cpu-setup is done.. it goes into loop of blinking a led. It works, in debugger (clocked from Cyclone Pro), but then I'm skipping the cpu_setup since it's been clocked from Cyclone Pro instead then by 9.8304MHz I get a LED-toggle frequency of about 240KHz..which seems a bit slow too. But that's is not why I'm asking so, never mind that
/Johan Sandgren
Svep Design Center AB
Lund, Sweden
+46 701 73 41 52

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