18F4431 how many PWM's ???

aaaaamartin · Joined: 17 Apr 2005 Posts: 39 Location: Germany Stuttgart

Hello,

I was wondering, after looking through some posts...

How many independent PWM channels has the 18F4431 ?
Datasheet says 8.

How independent are these ?
All run the same frequency but different duty cycles.

Thanks Martin

MikeValencia · Joined: 04 Aug 2004 Posts: 238 Location: Chicago

I looked into the 18F4431, and yes, they are all independent PWM channels, but I think they have a common period. You can get 8 independent channels, or 4 pairs of 'half bridge' PWMs, which means pwm0 and pwm1 are complements of each other, similiarly pwm2 and pwm3, pwm4 and pwm5, pwm6 and pwm7 (when one's high, the other one's low). In fact, perhaps there is also a CCP1, which may or may not be a truly independent channel from the other eight.

One thing i don't like about the 18F4431 is that it can only have 16K of ROM.

Did you know that the PIC18F8520 has FOUR independent PWMs (but with a common period)?

aaaaamartin · Joined: 17 Apr 2005 Posts: 39 Location: Germany Stuttgart

In a message dated 9/8/2005 11:31:19 AM Central Daylight Time, m.wochinger@gmx.de writes:
Hi Mike,

may you please further explain your post:

http://www.ccsinfo.com/forum/viewtopic.php?t=24307

I have had a look, and datasheet says, it has 4 duty-cycle registers.

All I want to do is drive DC-Brushed Motors.
They only need one PWM Pin each.
Can I drive 8 Motors simultaniously ?
Where do you read, all 8 PWM pins can run differnet dutycycles.

Thanks for looking again

aaaaamartin

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Hi Martin,

My father (who also happens to be my partner) was planning on using the 18F4431 to get 6 independent PWMs. Now that you pointed this out, it looks like 8 PWMs can only be obtained as 4 complementary pairs (half bridge mode). And with only 4 duty cycle generators, looks like we're limited to 4 independent single PWMs.

I'm going to ask Microchip tech support if there is indeed any PIC with more than 4 independent PWMs.

(Why not use two PICs?)

MikeValencia · Joined: 04 Aug 2004 Posts: 238 Location: Chicago

Microchip Tech Support has clarified the question:

Guest · Posted: Fri Sep 09, 2005 7:44 pm

aaaaaamarin:

The odd and the even PWM output pins are driven with a single PWM duty cycle generator. PWM1 The odd and the even PWM output pins are driven with a single PWM duty cycle generator. PWM1
The odd and the even PWM output pins are driven with a single PWM duty cycle generator. PWM1

= 3 x !

hitchi h8s has 8.

Thanks Martin