MC908LJ24 PLL stopped working after flash programming mistake

Discussion created by Guest on Apr 3, 2013



I'm working on reprogramming a multi-function gauge, and with the original gauge board I was reprogramming I wasn't able to get into Monitor mode using the blank reset vector and 32.768kHz clock.


I ended up using a different gauge, and initially I was able to use the PLL to get into monitor mode (reset vector blank and IRQ to GND). However, I made a programming mistake and didn't set the interrupt mask while doing some flash programming and an interrupt occurred, causing the board to lock up.


I've had this problem a couple times, and whenever it has happened I cannot get the chip into Monitor mode using any method for about an hour. IRQ to vTST and a high frequency crystal doesn't work either. However, after I take the dog for a walk or leave and come back, the chip will start working. However, with the second board after I had it lock up and become inaccessible for a bit I can no longer use the PLL in either Monitor mode with a blank reset vector, or in user mode (forced to use high frequency crystal and vTST on IRQ).


Anyone know why this is happening? Is the chip damaged permanently in regards to the usage of the PLL? What is happening that the chip needs to "rest" before it can be used again?


Thanks in advance,