Operating CCP1 and CCP2 of PIC 16F877A using C programming

[safwat]

i thought you said i have to use a power pwm control module to produce shifting signal in pic18f4431. thats why i am trying 1st to find out how the power control pwm works and how to generate them. then when i generate them i will try to shift. i am just trying to go step by step.

[Ttelmah]

Visualise:

With one channel of the power PWM, you can produce two signals that are the complement of one another.
You can invert the second signal, so you then get two signals that are the same from one PWM.
You can separately program the 'dead time', giving you the ability to delay the rising edge of the second signal from the first, and the falling edge from the first.
This then potentially gives from one power PWM channel, some range of shifted signals.

You are ignoring Temtronic's request to actually tell us what the relationship of the signals wants to be?.

Without some details, we are guessing. If you want to learn of the capabilities of the power PWM, as already said, look at the data sheet, example etc., and see what happens if you select to invert the second waveform, and change the deadtime settings.

[PCM programmer]

[safwat]

here is the answer to temtronics question (as much as i know until now)

1)as you know i want to generate two PWM signals with phase shift among them.
2) i want to use a 20 MHz crystal generating 20 kHz PWM, duty can be kept constant.
3)the phase shift will vary. i will vary the phase shift with adc. for example if i want a 25us phase shift then from outside by the use of a button i am gonna change the shift to 25us.

As the PIC has other things to do such as adc a normal delay/counter tactics wont work. So i need the PWM modules, and as Ttelmah said phase shift is impossible using PWM modules of pic 16f877a because both use same timer, i changed to PIC 18f4431.

this signals will later be used in the switch for a dc to dc converter.

i hope this gives you some idea, if not please ask specific questions.
thank you

[Ttelmah]

No guarantees on this, but you need something like:

[safwat]

Hey Ttelmah,
Thanks for your code. I am currently trying to decipher your code. Some of the things are going way over my head for a second year student like me. So i am trying understand the datasheet.

Anyways, I want to buy some new controllers. Can you suggest me some micro controller which does this phase shifting quite easily (I mean easier than pic18f4431).
Thank you.

[Ttelmah]

The basis of what I posted is pretty simple. The two PWM's run off two oscillators. To update the shift, I wait for one oscillator to reset to zero, wait for the required delay, and then reset the other oscillator. They then keep running with the required relationship.

The first peripheral that does potentially allow this is the COG. This is designed to produce two complementary signals, from one signal. This has programmable rising edge delays, and falling edge delays, from the source signal. However the second one that is really designed to do this is the PSMC module. This allows a single PWM, to have multiple outputs, with separately programmed start and end points. Change these, and you shift the output waveforms relative to one another.

Look for a chip with this The PIC16LF1784 for example. You change the 16bit phase register, to shift the position of the start event.

I have to ask what you actually want to 'do' with these phase shifted signals?. It is such an unusual 'need', that I wonder. Most people in the past who start wanting phase shifted signals really don't need them.
It's worth realising that normally phase shift implies working with something like analog or simulated analog signals. For example BLDC control that requires 3*60 degree phase shifted signals, is normally done by using three standard 'in phase' PWM signals at a higher frequency, and using these to synthesise the required output waveforms by just modulating the mark/space ratio of the three generators.
I must admit that if I wanted signals with a programmable relationship between them, I'd probably just use something like the AD9501 to delay the second signal.

[safwat]

this is the formula to calculate power PWM period in Datasheet for 4431

TPWM = [(PTPER - 1) * PTMRPS] / (Fosc / 4)

i suppose PTPER is 249 in your code?

and i searched through data sheet for PTMRPS but the only place i found is n the formula.

what is PTMRPS? what is its value in your code?

thanks

[PCM programmer]

How about Google ? Google it:

[safwat]

answer to Ttelmah
i need to pass this two signals into the gates of a full bridge DC to DC converter. i have read a paper about this which says phase shifted signal into the gates of a DC to DC converter is much more efficient. thats why i want to check it out

[safwat]

okay i think i found it, PTMRPS is the post scale value

[Ttelmah]

OK. PSFB.
Very different from what you have perhaps been talking about. You were saying 'duty could be constant', but for this duty _must_ be constant.
You actually need two pairs of 50% duty 180 degree signals, and then to adjust the overlap of these pairs. The overlap determines the energy transferred. This is what the CWG/COG peripheral is designed to generate. Look for a PIC with this. If it has an ECCP, then program this to generate one pair at 50% duty, and then program the COG to adjust the rising edge and falling edge delays together to provide the overlap adjustment.

[PCM programmer]