Unwanted output signal jitter

[LinkMTech]

Hello everyone,
First of all, thank you all for sharing your time and wisdom so others can excel.

I'm making a fuel injection circuit using the PIC16F737 that would allow me to control the outputs ON/OFF +/-. After gleaning the data specs on my part for understanding and researching this forum to get me this far plus experimentally trying different ideas, I hoped that an expert would be able to spot why I'm experiencing this unwanted signal jitter.
Attached are:
1. Copy of sample code working just one input. You'll notice that the ADC settings are not the usual settings but were left this way because I got a nicer response from the pot control. This might also be the band aid to the problem.

2. Scope screen shot of ouput signal with ON time delayed and with unwanted jitter at opposite end. If I turn the pot CCW from center, the output turn ON delay is increased from 0 to 500us.

3. Scope screen shot of ouput signal with OFF time delayed and with unwanted jitter at opposite end. If I turn the pot CW from center, the output turn OFF delay is increased from 0 to 500us.
The top trace (Yellow) is the input, bottom trace (Blue) is the output.

Input signal is 5V with 2.5ms LOW pulse and 20K pull up, pot is a 5K from 5V to GND. Output driving a current limited LED at the moment.

[skimask]

Hello everyone,
2. Scope screen shot of ouput signal with ON time delayed and with unwanted jitter at opposite end. If I turn the pot CCW from center, the output turn ON delay is increased from 0 to 500us.
3. Scope screen shot of ouput signal with OFF time delayed and with unwanted jitter at opposite end. If I turn the pot CW from center, the output turn OFF delay is increased from 0 to 500us.
The top trace (Yellow) is the input, bottom trace (Blue) is the output.
Input signal is 5V with 2.5ms LOW pulse and 20K pull up, pot is a 5K from 5V to GND. Output driving a current limited LED at the moment.

At first glance, your loops take different paths at different times, therefore, different numbers of instruction cycles. Look at your .lst file, count them up for the different if/then possibilities. You might need to throw a @nop in here or there to keep the timing correct.
Your 'jitter' is 500ns, which happens to be one instruction cycle at 8Mhz (2Mhz instruction rate). Which also happens to be the difference between a NOP (one cycle) and a GOTO (2 cycles).

[mister_e]

euhh 500 uSec Skimask, which is way over a NOP or GOTO

[skimask]

euhh 500 uSec Skimask, which is way over a NOP or GOTO

Yep, sure is...but that u looked so much like an n.
...unless the PIC is running at 8Khz

[LinkMTech]

Yep, sure is...but that u looked so much like an n.
...unless the PIC is running at 8Khz

I'm glad I'm not the only one that sees things!

[LinkMTech]

Just remembered something about the jitter...
If I commented the ADCIN command from the internal loop and just relied on the initial ADCIN read at the start of the program, the variable adjustment wouldn't work of course but be fixed at the pot setting instead and would get a clean output signal.
I read through the ADC section of the data specs that specified Rs be less than 10K, my pot is 5K and left me thinking the sampling time has to be set correctly.
Am I getting close or still wandering in the dark with a LED on a 2V battery?