I did not understand your question before (and still do not know what you are trying to do or what your TX source is?). During Sleep, the BRG is inactive (the clock to USART is suspended) so you cannot wakeup and catch incoming data automatically.
A couple options to consider:
1)You could tie your RX pin to one of the PORTB “wake on change” pins as you suggest, but it sounds like this is a board change for you. Doing this, you can wakeup your PIC with a toggle of the line into your RX pin and then be ready to catch data. Obviously, you would need to be able to toggle the line from the source – is this an option?
2)You could switch to the almost identical 18F4520. This PIC for the most part is PIN for PIN compatible, but has some neat advanced power management modes that enable the clock to the EUSART to be on when in reduced power mode. It also has an Auto-Wake-Up from Sleep feature that works essentially the same as option 1, except it all happens on the RX pin.
One last note - the 18F4520 is more feature rich and costs about 30% less than the 18F452.
Good Luck
Paul Borgmeier
Salt Lake City, UT
USA
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