Problem: Reset causes MC9S12E128 crystal to stop!

[NigelL]

Hi, I would appreciate it if anyone could suggest a cause for the following unusual problem.

I have a board with an MC9S12E128 80-pin processor on it and the crystal starts up properly every time I power up the board (i.e. cold boot).  However, if I ever activate the reset line (warm boot) this always causes the crystal to stop oscillating and the processor continues operating from its internal oscillator.

I have replaced the microprocessor, tried various crystal manufacturers and verified the PLL components, all without success...  The only remaining issue that I can think of is the layout of the PCB.  I am using a 4-layer PCB with a solid ground plane and I do not have any "noisy" supplies or traces routed anywhere near the crystal or PLL filter components.

I am using a 3.6864MHz crystal, PLL set to boost speed to 11.0592MHz, I have a 4k7 pull-up resistor on the /RESET line and my VCC is 3.3V.

Regards, NigelL

[eeetee]

hi:

i'm not sure this is your issue but check it out.

pin 26 (PE7) should be referenced to ground. i can't recall the exact signal name, but on reset the pll section checks the status of the pin and it should be at ground. you can use a 10k resistor to pull it low and then use it for any i/o in the application after.

regards,

ed

[NigelL]

Hi Ed

Thanks - that was the problem!  Somehow I managed to miss that description of the XCLKS line.

Regards, Nigel