PLL LOCK

[prog_ram]

Hello,

I am using the HCS12 (DP512), I did a board using this MCU with 16Mhz Crystal and 24Mhz bus speed so I used the PLL circuit. the board worked perfectly.

I wanted to do another board (with less pins usage) and with the same PCB layout for the crystal and the PLL filter and other basic circuit necessary for the MCU to function.

something went wrong and I had a shortcut, and the MCU got hot (not too much, but enough to know that there is something wrong). I fixed the problem and power on the board again, I could be able to flash the code and use the debugging tools (BDM communication works perfectly) and everything was fine except that the PLL didn't lock  at all and the code is waiting for the PLL to lock.

while (!(CLKSEL&0x80));  /* Wait for PLL to lock */

my explanation is that the shortcut was the reason since I used the same code for the PLL and the same filter values (obtained from the Freescale PLL filter calculator) which are proven to be working (in the previous board). the question is:

is it possible that the shortcut damaged the PLL circuit in the MCU?

is it possible that a circuit may get damaged and others do not inside the MCU, (for example, the timers are working but the SCI are not)?

thank you.

[Alban]

Hello,

Yes it is totally possible to only damage part of the µc, like the PLL filter.
May be, you damaged the internal circuitry on your µc when you did the short circuit.

To try and limit this in the future, use a current limited power supply.
I will not prevent all damages as it depends where you do the short circuit, but it will limit the damage on the board.

Alban.

[prog_ram]

thanks Alban for the reply, it's always helpful.