the problem of s12xdp512's external oscillator

[jennyroma]

hello.

now i have a problem ,

when i use usb mutilink BDM load codes into cpu, i found the codewarrior 4.5 tells me that the cpu works at 1.48M,when i check the regesiters and found it works in SCM mode.

the crystal wave seems not too nice when i use oscillograph determine the crystal pins.

even i didn't use PLL.by the way, the external oscillator i use is 8M,two capacitances value is 18pf and 22pf. the parallel conection resistance is 10M.

anyone can tell me what the problem is ?

is the oscillator circiut correct?

best wishes

[Steve]

You should firstly check that you have selected the correct oscillator type. If you have a bypass resistor then you should using the full-swing Pierce mode - check the status of the XCLKS pin at reset.

In most cases the load capacitors are the same value so check that your choice is correct for your crystal. Finally, there are recommended layouts for the oscillator circuit in Appendix C, you should compare these with your layout to make sure that you are not introducing unexpected circuit elements that will disrupt the oscillation.

In general placing an oscilloscope probe onto a crystal circuit will disturb its operation unless you are using a specialist probe with a very low input capacitance (<1pF).