I have some PIC18F1220 which I thought I would use up on a project.
In testing an output using a delay routine obtained from https://www.golovchenko.org/home/delay_loops , which I have used several times in the past, The time was entirely different from what it should be.
I made sure I had the system clock set OK, i.e. OSCCON = 0x60 (4Mhz) and CONFIG OSC= INTIO1 in order to 'scope the output on pin RA6.
Using the recently acquired FNIRS1-1013D, the wave form on RA6 displayed 2.32Khz?
I have used this PIC in past and do not recall any issues like this?
Any ideas of being something stupidly simple?

 

I have some PIC18F1220 which I thought I would use up on a project.
In testing an output using a delay routine obtained from https://www.golovchenko.org/home/delay_loops , which I have used several times in the past, The time was entirely different from what it should be.
I made sure I had the system clock set OK, i.e. OSCCON = 0x60 (4Mhz) and CONFIG OSC= INTIO1 in order to 'scope the output on pin RA6.
Using the recently acquired FNIRS1-1013D, the wave form on RA6 displayed 2.32Khz?
I have used this PIC in past and do not recall any issues like this?
Any ideas of being something stupidly simple?

Just a thought.
Try setting the oscilloscope TIME/DIV to the shortest time (highest frequency) and then switch it till you see the waveform.

 

Just a thought.
Try setting the oscilloscope TIME/DIV to the shortest time (highest frequency) and then switch it till you see the waveform.

Damn it Sir! you were right!
The lower Freq. must have been an harmonic?
So now why doesn't the delay loops show correct, Maybe I need to do the same!!

 

Yes. This confused me recently. It is the same phenomenon as undersampling at too low sampling rate. The reconstructed signal is folded back to a lower frequency, what we call aliasing.

 

I have some PIC18F1220 which I thought I would use up on a project.
In testing an output using a delay routine obtained from https://www.golovchenko.org/home/delay_loops , which I have used several times in the past, The time was entirely different from what it should be.
I made sure I had the system clock set OK, i.e. OSCCON = 0x60 (4Mhz) and CONFIG OSC= INTIO1 in order to 'scope the output on pin RA6.
Using the recently acquired FNIRS1-1013D, the wave form on RA6 displayed 2.32Khz?
I have used this PIC in past and do not recall any issues like this?
Any ideas of being something stupidly simple?

Add this: OSCCON=0b01100000; // 4Mhz internal clock

Never mind, seems you have the problem solved if you're actually getting the correct frequency on RA6.

 

Just a thought.
Try setting the oscilloscope TIME/DIV to the shortest time (highest frequency) and then switch it till you see the waveform.

I saw this many years ago when trying to look at a 40MHz clock with the scope down in the kHz range. The first clue was that, even though I was seeing what looked like a valid signal, I couldn't trigger properly. No matter where I set the trigger threshhold, the waveform would wander. Only as I turned up the sweep rate did I see what was going on.