Having issues trying to get some UART communication to run on a mega88PA, I decided to check the clock. Board is working fine otherwise, apart from the UART.
I have a minimal board, dead stable 3.3V to VCC and AVCC, proper decoupling, brand new device, erased, fuses set to CLKDIV8 and to output clock on CLKO.
The clock frequency is correct at 1MHz, but I have 60-80% clock jitter, it's so unstable, my scope can hardly show the signal. No wonder the UART won't work with this.
Same throughout the supply range from 1.6 to 5V
Adding a simple while loop in the code doesn't help either.
I've been trough the datasheet to see if there's any difference in the clock system between the mega8, mega88 and mega88PA, and although there is obviously differences, theres nothing that should cause this.
I've tried 3 devices now, all with the same result.
I suspect my devices are bad.
Or did I miss something somewhere?