Pwm and clock speed

[retepsnikrep]

Just a quicky.

I want to program an 08M to provide a 2khz 25% duty pwm signal from the pwm pin.

Using the wizard I found 2khz was too low, but I could acheive 4khz with 4mhz clock, so I am using the 4khz setting but then underclocking the pic to 2mhz.

Will this acheive what I require?

It looks reasonable on the scope, frequency appears OK, but I was a bit worried about the duty, is the duty number a counter/timer?

So If for instance duty is 100 (example number) but underclocked to 2mhz it actually takes twice as long to count the duty period?

So should I have changed duty to 50 (halved it) as well as underclocking chip to maintain the duty interval with correct frequency?

 

[BeanieBots]

No, the duty will remain at whatever you set it to.
Changing the clock to half will halve the PWM frequency but the duty will remain the same.

 

[eclectic]

Peter.
Another idea, keeping your Picaxe at “normal” speed.

Based on Dippy's posting here:
http://www.picaxeforum.co.uk/showthread.php?t=5872&highlight=jeremy+pwm

Try the following two programs,
and view the results on your 'scope

#picaxe 08m

looper:
pwmout 2,124,125 ; 8kHz from Wizard
peek $12,b1
sertxd ("Normal: ",#b1,13,10)
pause 4000
b1 = b1 + 1			' add 1 (bin 1)
poke $12, b1
peek $12,b1			' peek to confirm
sertxd ("Prescale / 4: b1= ",#b1,13,10)

pause 4000
goto looper

Which can then be shortened to:

#picaxe 08m

pwmout 2,124,125
poke $12,5

do
; the rest of your program here
loop

e

 

[retepsnikrep]

Brilliant as usual. Thanks