18f2580 with EUSART...can't wake up from sleep

lubom · Joined: 20 Apr 2006 Posts: 6

Hi iam am trying to make 18f2580 to wake up from sleep every i send a character over pc serial port here is the part of code:

Ttelmah · Guest

There are limitations to this ability. The clock needs to wake fast enough for the character to be received, when the falling edge of the start bit is detected. There are therfore severe limitations on doing this with some oscillator sources. You might be better off putting the chip into 'PRI_IDLE' mode, rather than fully asleep, which will leave just the oscillator running.
Why are you clearing the interrupt in the main loop?. When you 'sleep', the next instruction is 'prefetched, and normally this is executed before the interrupt is actually serviced. I wonder what the effect of having an interupt 'clear' prefetched will be? The interrupt will be cleared in the handler, so I'd personally just put a 'nop' after the sleep (delay_cycles(1)).

Best Wishes

Assen · Joined: 18 Oct 2006 Posts: 8

I think the problem here is that the main loop is going so fast that there is no time to receive a char. When the micro wake up from the strarting edge then new cycle in the main loop go back to sleep and that stops the oscillator and the micro is not able to receive the char. You have to put delay of at least 1 char time before going back to sleep.