Simple Frequency meter.
This program is a simple one-bit logical analyzer. It probes the bit 7 of port A and keep track of state changes on that input. For each change (0 to 1 or 1 to 0 transition), it keeps track of the free running counter (TCNT). After collecting the samples, it report them on the serial line.
I have used this simple logical analyzer to debug my parallel port eprom programmer. I connected the PA7 input to the CE, OE or PGM eprom pin. I was able to measure the 1ms pulse that I applied on the PGM pin.
The accuracy of level change by the analyzer is in the order of 50us with a 8Mhz 68HC11. So, don't expect to analyze frequencies above 10Khz (due to Shannon).
Source file: freqmeter.c