On Tue, 4 Nov 2003 20:12:02 +0530, you wrote:

>Hi,
>
>Summary: Should I use interrupts to do all time-based activities that a
>PIC does ?...
>
>I've just finished coding and testing a PIC project that was ~10 months
>in making. It has an LCD, 4-key keypad, temperature sensor, optos, LEDs
>etc. - A PID temperature controller. The controller accepts setpoints
>for timer, temperature, Kp, Ki and Kd. The timer can count from 1 second
>to 999.59 minute. The duty cycle for the opto is approximately 0.25
>seconds (1 ms x 255).
>
>The loop runs like this:
>1. Display the actual temperature and timer,
>2. Take an ADC reading,
>3. Calculate PWM,
>4. Run opto for that long,
>5. Store the current timer values in EEPROM,
>6. Check if the user has pressed any key and depending on it do
>something. Keypress is monitored all the while by PortB interrupt on
>change and only after steps 1-5 are over, it acts on what key is
>pressed.
>
>Everything works fine, it accepts user inputs, calculates PWM, runs
>opto, monitors key presses, shows current timer. The problem is...
>
>I run the loops sequentially, so it does one thing at a time. So even if
>the PIC is in the middle of running the opto and a timer second crosses
>over, the display is refreshed much later when duty cycle is over. And
>it looks as if the timer is irregular. Further, there is a major fault
>in the system that the PWM runs discontinuously - LCD display, EEPROM
>save, ADC reading are outside the duty cycle.
>
>My question is, should I use interrupts to do these activities?
>1. Inside the interrupt routine have a counter and flag for each of the
>above activity. 2. Every millisecond, update the flags. 3. After
>returning from the millisecond interrupt, check flags and do relevant
>activities.
>
>Will this be a _good_ design? I mean, everything being interrupt driven.
>
>The post is a bit too verbose for my liking, but I'd like to make my
>problem very clear. Sorry...
>
>Thanks,
>Mohit.

You should certainly do the PWM under interrupts, as this will guarantee =
consistent timing.=20
You may also want to do the ADC reading as well, so it happens at =
consistent intervals.

The other stuff will be less time-critical, so it won't really matter =
when you do them.

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