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Forum Index : Microcontroller and PC projects : MMX: Turning off PWM
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| BrantB Newbie  Joined: 27/10/2017 Location: CanadaPosts: 40 |
Hello All, Sorry for another post/topic, so quickly (I just recently posted one about the GPS functions), but I have run into another little snag - completely unrelated to the GPS issue. This time, it is with PWM-ing a LED. Simple enough; I've done it 100's or 1000's of times. But ... When I issue PWM 2, 500, 100, I get a nice bright LED. When I issue PWM 2, 500, 1, I get a dim LED. All good; all exactly as expected. When I issue PWM 2, 500, 0, I get ... a bright LED. Huh?   What I expected was no signal at all (i.e., LED completely off). I can get the LED to be extremely dim by using a value of 0.1 - but once I turn on the PWM, I can never seem to get it fully turned off again. I also tried PWM OFF, but that gives a syntax error. I tried PWM 2, 500, 0 in Micromite "Standard" on an MX170 (DIP-28), and it behaved exactly as I expected - it turned the LED off completely. Has anyone else encountered this? Any ideas? By the way, my current MMX environment (in which I am experiencing the PWM issue) is as follows: PIC32MZ2048EFH100 processor OPTION CPU 200 OPTION LCDPANEL ILI9341_16_BUFF, 98 OPTION HEARTBEAT ON MMX Version 5.4.14 Cheers! Brant |
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| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 10569 |
Hi Brant Nice to see someone using the MMX. Bedtime here in the UK but I'll look at both issues tomorrow Peter |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10569 |
This seems to be a difference in the Microchip plib routines between the old plib library and the new Harmony plib calls. My code is correctly calling the plib routine with the value 0 but it is being ignored/misinterpreted. I will need to special case 0 to fix the issue. I'll post an update later today. NB the correct syntax to stop a PWM output is PWM n,STOP Bug fix here |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
Don't you have to make the pin go inactive (open) to insure 'offness' ? Or does STOP do that ? |
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| LouisG Senior Member  Joined: 19/03/2016 Location: AustraliaPosts: 129 |
PWM n,STOP To me STOP has connotations of STOP FLIPPING continuously between logic 1 and logic 0. I haven't tried the PWM command till now but could it conceivably stop at logic 1? |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10569 |
PWM n,STOP is standard Micromite syntax - see the Micromite manual The pin is released back to the default state (input) - this is the same for MM, MM+ and MMX The only thing differences in the MMX was that prior to this patch setting the duty cycle to zero was being incorrectly handled and the MMX has one extra pin on channel 2 |
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| BrantB Newbie Joined: 27/10/2017 Location: CanadaPosts: 40 |
@matherp, I have some bad news - the updated firmware does not appear to have fixed up the issue(s)  . It has changed the PWM behaviour associated with a 0 value, but it is still not right. With the firmware update applied, issuing PWM 2, 500, 0 now results in half brilliance, rather than pinning the LED at full brilliance the way it used to. But it does not turn it off. BTW - no change in the (mis)behaviour of the GPS function, either. But I will continue that discussion in the other (GPS) thread, for those who may only be following that one. Admittedly, I have not broken out my oscilloscope to confirm that PWM 0 results in precisely a 50% duty cycle. But by comparing the results of a 0 value to those of 40, 50, and 60, I would say 50 is a pretty good bet. The brilliance of the LED appears to remain the same when alternating between a PWM value of 0 and 50, whereas alternating between 0 and 40, or 0 and 60, does generate an easily perceptible difference. By the way - my bad about PWM OFF vs PWM n, STOP. In the prose section of the Micromite manual (v5.4, pg 38, to be precise), there is a reference to using the PWM OFF command. I must confess that, in that case, I failed to refer to the actual Command table (beginning on page 52). Oops.  Sorry about that.Using PWM 2, STOP does extinguish the LED - but, of course, as you know, that is not the equivalent of PWM 2, n, 0. The former also turns off all of the PWM signals running on #2, which may not be desirable ... whereas the latter would (for practical purposes) turn "off" just the one sub-channel of #2. Any chance you could have another look at this to see what's up? |
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| BrantB Newbie Joined: 27/10/2017 Location: CanadaPosts: 40 |
NOTE: This is a (purposeful) cross-posting of a message from my other (GPS) thread. The same info is relevant in both threads. @matherp, I take it all back! The firmware update is fine. I somehow screwed up  .I previously ended up re-burning exactly the same firmware (sigh). I wanted to keep the original version of the 5.4.14 hex file, just in case I needed to do further (comparative) troubleshooting. So, I created a copy with a new name. And after that, something went screwy - it looks like I somehow might have re-downloaded the earlier version of the ZIP file from the forum, instead of the correct/new one. Of course, since the version number didn't actually change, I was doomed. Anyway, I am very pleased to report that the error was mine, not yours, Peter. (Well, it does not please me that I goofed up like that  , but I am glad it turned out to be something so simple.)Why the PWM behaviour changed when I re-burned the same firmware, I will never know. At this point, I am content for that simply to remain a mystery. Anyone: This brings me to another question (about using the forum) - how do I edit my own messages? I see that others do it, and I have looked at the Help (which, in this case, is not helpful). I don't see an Edit button anywhere. I would like to edit my previous "no joy" message with a line at the top, to warn future readers that the information contained therein is not accurate. I don't want to erase my gaffe - there is no integrity in that. I did it; I will "own" it. But, I don't want to cause people grief with bad information. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2959 |
If it makes you feel any better, I have been using MicroMites for 4 years; and have programmed 100's, yet occasionally I still make this exact same mistake! |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
@BrantB, you can only edit your own post for a limited time or until someone adds another post below it. The Edit button will appear to the right of the Buddy button at the bottom of your post during this time. Paul in NY |
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| BrantB Newbie Joined: 27/10/2017 Location: CanadaPosts: 40 |
@WhiteWizzard: Many thanks for the consoling words. It makes me feel a little better knowing I am not alone.  @Paul_L (and credit also goes to @WhiteWizzard for your similar reply in the GPS thread): Thanks for the tip about the Edit. It was driving me nuts. |
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