My first foray into PWM

[Demon]

Before I get too deep in this, can I blink an LED ON for 500uS, OFF for 500uS using standard PWM module?

Or am I trying to use a Ferrari as a baby stroller?

I know I can use DT_INT but I know how to do that and want to avoid using cycles. The PWM hardware is there doing nothing and I was hoping I could use it as a heartbeat during my tests.

I've printed pages 186-189 of the 18F44K22 datasheet and it doesn't seem overwhelming at first glance. The only part I can't determine by reading that is if I can use it as slow as I want. I know this is meant to drive motors so it's entirely possible that it can't physically go this slow.

Robert


EDIT: I'm running at 64MHz so I can guarantee persistence of vision while blinking at least 50 LEDs, manage a keypad and handle USART comms (at the very least). But I'm getting a feeling by looking at that PWM PERIOD formula at 14-1 that I could only do this if I slow to a crawl.

[richard]

if you are using the hpwm command the max freq is 32767hz the min @64mhz ck is 3905 hz on a pic18
max period 256uS min 30.5uS
so you could at 50% duty get 128uS on 128uS off

[Demon]

Yes, I definitely want the hardware PWM. But it's not the 50% duty that I was concerned with, it was the 1 second period.

I see now the relation between clock speed and the PWM output. So there's no way I can get it slow enough to use it as a heartbeat (1 sec period) in the background if we limitted with a 4MHz lower range.

I was hoping to use it as a debugging tool; to show that a PIC is indeed working without taking any clock cycles (disturbing cycle sensitive logic). And I wanted to try out HPWM, I'm nowhere near ready to get back on my CNC project; have to complete my residential alarm system first (and I'd like to get that interfacing with android, text messenging and web page - lots of learning).

Robert

[Amoque]

You might, if you have one laying around, use a clock divider chip... or a counter... Here's a link that explains my thinking better than I can.

[richard]

You might be able to achieve something using compare mode and the external clock pin for timer1. if you have enough spare pins and if you were really clever
use the hpwm output to drive tmr1ck then you could change the flash rate on the fly

[Demon]

Euh, I think I'll just get back to finishing my Charlie-plexing work for now. LOL

Thanks though, I will have to jump into PWM one day, hopefully next summer.

Robert