Thanks a lot Kerry for the clarification. I guess this would mean=20
however that a 1 dimming level would effectively be a PWM signal at a=20
frequency of 24kHz/64 =3D 375 Hz (assuming the 10 bit PWM is 24 kHz) . The=
=20
reason I am so concerned about the low level ie. 1 is that my=20
application is LED dimming at a high frequency. Currently my LED at a=20
PWM level of 1/1024 snaps on at too high a level. I would like it to=20
come on lower at the first level of dimming. 375 Hz is too low a=20
frequency for my application.

Jim


On 2017-09-07 12:56 PM, Kerry wrote:
> OK, I got some numbers wrong.
>
> If your 16bit value was 0x3000, then the 10bit would be 0x0c0 and the
> 6bit would be 0.
> The PWM output would be 192/1024 for all cycles, so there would be no
> dithering.  But 192/1024 is exactly equal to 12288/65536, so no
> dithering is needed.
>
> That's what I get for doing hex arithmetic in my head!
>
> Kerry
>
>
> On 9/7/2017 11:26 AM, Kerry wrote:
>> I guess I should have been more clear.
>>
>> The leftmost 10 bits becomes the variable 10bit and the rightmost 6 bits
>> becomes the variable 6bit, as in:
>>
>> 16bit =3D 0x1234 =3D 0b0001 0010 0011 0100
>> 10bit =3D 0b0001 0010 00 =3D 0x0048
>> 6bit =3D 0b11 0100 =3D 0x34
>>
>> If your 16bit value was 0x0001, then the 10bit would be 0 and the 6bit
>> would be 1.
>> The PWM output would be 0 for 63 cycles, the 1/1024 for 1 cycle.
>> If your 16bit value was 0x3000, then the 10bit would be 0x300 and the
>> 6bit would be 0.
>> The PWM output would be 768/1024 for all cycles, so there would be no
>> dithering.  But 768/1024 is exactly equal to 12288/65536, so no
>> dithering is needed.
>>
>> Does that help?
>>
>> Kerry
>>
>>
>> On 9/7/2017 12:26 AM, Jim Ruxton wrote:
>>> Thanks Kerry,
>>>
>>> This looks interesting , I don't quite follow it however.  How would
>>> this work if my 16 bit value was 0x0001 for example. In that case there
>>> would be no dithering would there as the 6 bit value would be 0 so I
>>> would be left with 10 bit PWM or am I missing something here. Thanks fo=
r
>>> any clarification.
>>>
>>> Jim
>>>
>>>
>>>
>>> On 2017-09-06 07:41 PM, Kerry wrote:
>>>> I think you would need to dither it.
>>>>
>>>> Set up an interrupt for each PWM cycle.  Separate the 16 bit word into
>>>> 10bit and 6bit.
>>>>
>>>> In interrupt:
>>>> Acc +=3D 6bit;
>>>> if(Acc>0x3f)    // If bit 7 set
>>>> {
>>>>          Acc &=3D 0x3f;    // Clear 7th bit
>>>>          set_PWM(10bit+1);    // Extra long cycle
>>>> }
>>>> else
>>>>          set_PWM(10bit);    // "Normal" cycle
>>>>
>>>>
>>>> It will average out to your 16 bit value.
>>>>
>>>> Kerry
>>>>
>>>>
>>>>
>>>>
>>>> On 9/6/2017 4:41 PM, Jim Ruxton wrote:
>>>>> I got a reality check today when I thought I would try setting up a P=
IC
>>>>> for 24 KHz 16 bit PWM . I had been using 10 bit and wanted to up the
>>>>> resolution. After doing some calculations using something like the PI=
C
>>>>> 16F1779 with integrated 16 bit PWM , I would require a 1.6 GHz clock =
to
>>>>> achieve 16 bits at 24 kHz . Just curious what other folks would use f=
or
>>>>> such an application. Highest frequency one could get using 16 bit PWM
>>>>> with a  32 MHz clock is about 488 Hz.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Jim
>>>>>

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.