Listing 1—The PBasic pseudo code shows how an approximate 30-MHz signal is measured using a relatively low-power 4-MHz microprocessor. The design uses the PIC16F877A’s internal Timer0 with a built-in prescaler. 
fhilo var word			//Contains RF frequency after measurement
measrf:
	High PORTE.1			//Enable RF oscillator gate
	Low PORTA.5			//Disable t0ckl gate
	LowPORTE.0			//Force local oscillator gate output high
	TMR0=0				//Clear TIMER0
	PULSOUT PORTA.5,100 		//Enable tockl gate for 1 ms 
	Low PORTE.1			//Disable RF oscillator gate
	fhilo.byte1=TMR0			//Extract upper 8 bits of Timer0
	call extract			//Extract value in prescaler
	RETURN
extract:	
		For I=1 to 255			//Pulse Timer0 until prescaler overflows
		PULSOUT PORTA.5,1
		If TMR0-fhilo.byte1=1 then goto done 	//Is there overflow?
		Next I				//No
done:	fhilo.byte0=256-I				//Yes. 256 – number of loop cycles = prescaler value
	Return