x. Impulse width measurement: ECCP PWM Meter Example for PIC18F2550, PIC18F24J50 and PIC18F26J50

PIC18 microcontrollers have two (E)CCP units that can operate in three mores: capture, compare and PWM (pulse width modulation). Here is an example on how to program PIC18F2550 CCP unit to measure pulse width. A special *.HEX file, PIC18F2550 firmware v2.6.hex is provided in Downloads section. The example code together with DLL library v3.8 are in ECCP PWM Meter.zip. The timer 1 is used to provide clock for the CCP2 unit. The CC2 button reconfigures timer 1 to produce clock signal with 500 kHz instead of default signal with 1 MHz. Note that CCP2 measures impulse width with a 16-bit resolution. Therefore it is important to adapt the timer 1 clock frequency to use the most of the 16-bit range to achieve higher measurement result accuracy.

The pulse width in impulses can easily be converted in seconds by multiplying it with the length of a clock impulse. If the timer 1 is running on 1 MHz, the clock impulse lasts exactly 1 microsecond.

The original example (get ECCP PWM Meter (x64).zip Downloads section) below is based on a modified Velleman K8055-1 board with PIC18F2550, 4 MHz XTAL crystal and R35 resistor removed.