PWM irregularity??

[fusian]

i try to test my PWM output on CCP1 by sending command via USART. it works perfectly with input from 0 to 128, but when i enter 129 the voltmeter reads 0!!
surprisingly, a 255 return a max voltage of 5V...so, for my case it somehow works from 0 to 128 and 255...weird??
for your info, the detected 8bits input command from USART is directly written to CCPR1L...

 

[Nigel Goodwin]

What resolution do you have the PWM set to?, resolution is also dependent on PWM speed, the faster it runs the less resolution you have.

 

[fusian]

i use 20MHZ crystal , 19.53KHz PWM, 10bits resolution...but only use the MSB 8bits in CCPR1L...is this setting that cause the irregularity that i am facing??

 

[Nigel Goodwin]

Assuming you're setting it up correctly then, for a start isolate which part is giving the problem, the serial routines of the PWM - easy to do by hardcoding 129 in the program to be written to the PWM.

But it still sounds like the PWM may be set to the wrong resolution?, I would double and triple check that, and post the code here (using the 'code' tags to maintain formatting).

 

[fusian]

i use 2 PWM, when CCP1 on, CCP2 off and vice-versa...