As typically done, to conserve power, electronic devices are put into a 'sleep' mode. For the RFM+PIC setup I had mentioned previously, the same method is employed. The PIC commands the RFM to go into sleep mode but preprogrammed the RFM to wake up in about 5s... very very short nap... after the RFM is commanded to sleep, PIC commanded itself to sleep indefinitely until awaken by something...
After the 5s nap, RFM will wake up (5% accuracy) and will pull the nIRQ line low. The nIRQ line is connected to one of PIC 'interrupt-on-change' pin. The change in voltage level wakes up the PIC and it will continue to execute exactly where it falls asleep.
2 days ago