here is an example of how you would execute it.

the mcu in question is running on 4Mhz internal RC (1us timer clicks). it is measuring the pulse width of a 100Khz pulse train (5us pulse width) and storing the number of internal clock ticks during the time T1G has gone low into count.

in this case, count = 5 is the right answer.

because of phase differences between the incoming pulse and the clock, you may have 1 or up to 2 ticks' errors. so to be very accurate, you have to increase the internal clock speed.

the limitation here is the length of the pulse. as tmr1 is a 16-bit timer, the max pulse length is 64K clock ticks. you can solve that by having an interrupt on tmr1 overflow and use a software counter to make the timer a 48-bit timer (16-bit hardware timer + 32-bit software timer).



(原文件名:12F675 Gated TMR1.PNG)

the same concept can also be easily implemented on any mcu with a gated timer, like the 8051.