Updating HPWM frequently, safe?

[skimask]

The µChip section Skimask pointed at shows " PMW module *might* be disabled before changing the dutycycle ". I read some Other Pics Datasheets and this GREY section didn't appear elsewhere ...

And I just downloaded the latest/greatest 12F683 datasheet and it DOESN'T have that statement in there. What's up with that?

µChip clearly says : Changing the dutycycle while PWM running (and only dutycycle is enough ) will produce unwanted effects ...
The only way I see to keep ( is it really necessary ??? Good Q.) a "neat" PWM output would be to switch between HPWM, to the last produced fixed freq. and duty, soft PWM ... while disabling CCP, changing Dutycycle and re-enabling the CCP.

Couldn't you update the duty cycle right after T2 has overflowed? As long as the duty cycle wasn't too low or too high, wouldn't this almost eliminate all false glitches?

Back to our Friend Skimask ... I really do not know ... if he really doesn't know the "what is wrong".

I got a good handle on "what's wrong" 'cause I ran into the same problem with my multi-channel software PWM program I wrote to run a bunch of lights awhile back. And my fix for the problem was to only update the PWM duty cycle for each channel in between cycles, so basically, I ended up with PWM that couldn't do 100% duty cycle, but only about 0%-95% duty cycle. The extra 5% at the top end was used to update the software registers.

[Acetronics2]

Hi, Skimask

Q1) Here is an excerpt ( joined ) ... Peu found it also ... If not in the latest datasheets, might we think the new devices have been modified ???

Q2) I must experiment ... T2 overflow is to try ... Honestly, I would use a SMD 16F628,648,88 or ??, instead, if size is a really a problem ( LOL !!! )

R3) It's the most logical solution ...

Regards
Alain

[peu]

Hi, Skimask

Q1) Here is an excerpt ( joined ) ... Peu found it also ... If not in the latest datasheets, might we think the new devices have been modified ???

Its indeed modified...!! I just redownloaded the datasheet and the PWM section is more complete now.

check both versions here: http://peu.net/temp/pic12f683_OLD_vs_NEW.zip

Q2) I must experiment ... T2 overflow is to try ... Honestly, I would use a SMD 16F628,648,88 or ??, instead, if size is a really a problem ( LOL !!! )

Well, in my case I have very low space, all my pcb is a 18mm diameter board...

Here is my code, I tidied / commented it so its more readable: http://peu.net/temp/pwm-adc

Thanks!

[Darrel Taylor]

And, You're all correct!

Well, except for that part about me being wrong

After my last post, I started working on an example for Pablo. It's kind of grown along the way, and is now a candidate for replacement of the HPWM command. IMHO

It pretty much encompasses everything you guys talked about while I was doing it. Plus maybe a bit more.

It's an Include file that gives 1 new command...

@  HPWM10  1, _DutyCycle, _Frequency

It works the same way as the PBP HPWM command, except that it uses 10-bit resolution, works with all CCP modules CCP1-CCP5, And is "Glitch-Free" when changing Frequency or DutyCycle.

Well, at least that's what it's supposed to do. Seems to work pretty good here, but I've only had a day to play with it.

It uses about 250 more words than HPWM, so I don't know how good it will be for a 12F683. But it definately will fit, if the rest of the program isn't too big.

If anyone has any problems, I'd appreciate a "Heads Up".

http://www.pbpgroup.com/files/HPWM10.zip
<br>

[peu]

OMG

Im "digesting" the code, just tried it and it compiles to 409words, compact enough for a 12f683

Thanks!!!

[mister_e]

Seems to work pretty good here, but I've only had a day to play with it.

One day to do all that? Wow, some 'over a month TicTacToe brain challenged programmer' will be impressed

[peu]

I just tested it using this code:

'       Pic Configuration
@ device pic12f683,INTRC_OSC_NOCLKOUT , wdt_on, mclr_off, protect_off        

'       Hardware configuration

'       I/Os
TRISIO = %00010010      ' pin1 is ADC , pin4 is the calibration button

'       ADC's
ANSEL = %00000010  
DEFINE ADC_BITS 10      ' ADCIN resolution  (Bits)
DEFINE ADC_CLOCK 1      ' ADC clock source  (Fosc/8)
DEFINE ADC_SAMPLEUS 11  ' ADC sampling time (uSec)                      
ADCON0.7 = 1            ' Right justified results

'       Comparator
'CMCON0 = %00000111     ' Disable comparator
'VRCON  = %00000000     ' disable
cmcon0 = %00001110      ' Multiplexed Input with Internal Reference CIS=1
vrcon  = %10001010      ' set vref=2.25v (from 4v input) 

include "HPWM10.pbp"

' definitions
pote 		var word
Frequency   var word  ' edited after original post per Darrel suggestion
calibraled  var gpio.5

gpio=0
frequency=1000
pause 50    ' coffee break

for pote=1 to 1023 

@ HPWM10  1, _pote, _Frequency
pause 10

'gosub flashled

next pote
end

flashled:
high calibraled     ' I use this to visually count each loop step
pause 50
low calibraled      ' by using it I saw that my switcher starts to 
pause 50            ' work at hpwm=4, less than that is too low
high calibraled
pause 50
low calibraled
pause 50
high calibraled
pause 50
low calibraled
pause 700
return

Comments:

I used the flashing led routine to know when my switcher started to work, it started at hpwm=4 which is great, the power led is very dim at this value.

then I removed the flashing routine and something was too fast, because my switcher was off. So I added a little pause in there and it was solved, tried 1, 5 and settled in 10ms where it started to work again.

This is great!, now I will test it with adcin

pablo

[T.Jackson]

One day to do all that? Wow, some 'over a month TicTacToe brain challenged programmer' will be impressed

Yes, Mister_e, very impressive indeed.