TIMERS

vijayan · Joined: 15 Nov 2005 Posts: 3

Greetings to all
ex_stwt.c,ex_stwt1.c,ex_stwt2 .c are examples for measuring time in
secs . Is it possible to measure time in ms and micro secs ? , if so
please help me . I am using 16f877a pic with 20Mhz oscillator --c.vijayan

Ttelmah · Guest

mSec yes. uSec, gets harder.
If the timer used in the example, is reprogrammed to trigger at mSec intervals (I think the examples use between about 50mSec, and 8mSec), then the 'tick', will give a measurement at this level. Going faster than mSec, starts to run into the problems of the latency involved in the interrupts themselves, and the percentage of the time, that the code is spending in the interrupt.
You can relatively easily measure to uSec levels using the hardware CTC, if the chip you are looking at offers one. If you look at EX_CCPMP, this shows this hardware being used to measure a pulse width to better than uSec accuracies (with some limitations on the widths that can be handled). For pulses longer than the timer period, a 'carry' counter will need to be generated as well.

Best Wishes