SPWM and Elapsed Timer

[Darrel Taylor]

Is there a better way to output a 82Hz PWM single than using your software routine. Your routine works perfect however I also need to read a frequency of 0-1kHz at the same time. With the resolution of 256 steps @ 82Hz its pretty interrupt hungry.

I'm sure there's a way to get what you need, but can you give me some more info to work with.

Which PIC?
What OSC?
How many SPWM channels?
What Freq is HPWM running at?
Is Timer0 available?
Which Pin is the 0-1khz on, and can it be moved?
Can whatever is on the T0CKI pin be moved?
Does it HAVE to be 82hz?
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[CocaColaKid]

Oh, guess I missed posting all the relevant information.

16F88 @ 10MHz
Single 82Hz SPWM Channel
Single 1kHz HPWM Channel
Timer0 - Free, Timer1 - SPWM , Timer2 - HPWM
The 1kHz HPWM is being output on portb.3, it could be either portb.0 or portb.3
The porta.4/T0CKI can be made available for use, its just an input
Unfortunately the 82Hz is required, its the control signal for an ECM motor

[Darrel Taylor]

Oh, guess I missed posting all the relevant information.

16F88 @ 10MHz
Single 82Hz SPWM Channel
Single 1kHz HPWM Channel
Timer0 - Free, Timer1 - SPWM , Timer2 - HPWM
The 1kHz HPWM is being output on portb.3, it could be either portb.0 or portb.3
The porta.4/T0CKI can be made available for use, its just an input
Unfortunately the 82Hz is required, its the control signal for an ECM motor

There ya go. Now there's some room to play with.
But now you'll regret saying you want to do it yourself.

Since there's only 1 SPWM channel. I would recommend reverting the the original SSPWM program. It only uses 2 interrupts per cycle, 1 for the ON time, and 1 for the OFF time. But it would need to be modified to work at 82hz, since it currently runs at 100. And in the SSPWM routines, you can create a 1sec period for timing the input frequency's measurement.

Then by feeding the 0-1khz into Timer 0 (T0CKI), you should get a real good count/frequency that works in the background, unlike the COUNT command.

[CocaColaKid]

Let me see if I get this right. Bare with me because I am still very green on the whole timer thing. I need to set Timer0 to count the pulses coming in on T0CKI for 1 second once a clock is seen. This 1 second interval will be determined from Timer1?

[Darrel Taylor]

That's the plan.

Of course, it doesn't have to be a 1 second sample period.
As long as it's a constant time base, readings can be easily corrected to match the difference.
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