PWM using 16F1824 and optional pins

[stephen haggas]

I am having problems with re-allocating the PWM pin to CCP2_A5. Also I am having to use timer 2, if I set Timer 6 as commented out I get no output. I presently get the PWM on C3.

What have I missed?

My code is as follows:

[asmboy]

#FUSES ??
check the header file and data sheet

this is an optional pin assign controlled by #fuses i believe

[Ttelmah]

OK, deep breath.

There are four different 'setups' of PIC's in this regard:

1) Most old PIC's, where all pins are fixed.
2) Some later chips, where the pins are re-mappable using fuses.
3) Newer chips where the some pins are configured using the device configuration.
4) Generally more complex chips with lots of peripherals where the pins are setup using #PIN_SELECT.

The 1824, is one of the third.
The critical question is 'what compiler version'?. Unfortunately, CCS has the habit of adding support for things like this, then not getting it working for a few compiler versions.

So real answer I'm afraid is to upgrade the compiler. Otherwise you need to set these bits yourself.

I can confirm that with the 4.137, the syntax as posted, _does_ correctly set the APFCON1.0 bit to select the PWM to A5, and does set bit 1, and clear bit 0 of the CCPTMRS1 register to select timer6.

There are a couple of other comments though, one which _will_ cause problems.

First, on line 2, get rid of the processor name. This is already set when you include the processor file, and having it in two places can lead to problems later if (for instance) you move the code to a different chip.

Then the clock settings. The chip _does not allow a external 32MHz crystal_ which is what you are configured for. 32MHz, can only be done by having an external 32MHz oscillator (EC fuse), or by using an 8Mhz crystal, and enabling the PLL. The maximum crystal frequency supported is 20MHz - Table 30-1 in the data sheet. If it is working, it is 'luck'.....

Best Wishes

[stephen haggas]

Thanks Ttelmah for your reply,

I now realise my mistake, I had set the clock as external, should of been INTRC_IO, which frees up RA5, so that APFCON1.0 now sets A5 to PWM output.

The problem with Timer 6 is on MPLAB SIM, when I reprogram the header AC2444043 Timer 6 now works.

Thanks for your help.

Regards,
Stephen

[Ttelmah]

Brilliant.
So the extra bit about the clock, pointed into the right direction, and "Robert's your parent's brother"...

Best Wishes

[ressas]

Hello, in the above code, I have

[Ttelmah]

[ressas]

Thank you. 16F1824 built-in oscillator 32MHz. Can I get 32MHZ frequency from pwm? What are the 'timer2' settings needed to get the highest frequency from the pwm pin?

[temtronic]

ressas

learn by reading, learn by doing !

Download the PIC dataheet, and read the PWM section. There are 3 simple equations that deal with period and duty cycle . Cut code to use them in your PIC and send the results to a PC or LCD module. Use the samples given by uChip in the chart to confirm your code is correct as 'braces' or () are important to get the numbers right. Once the code is correct, enter 00 or ff and see what frequency your PIC can do PWM.
This way YOU learn and be a better programmer

Jay

[Ttelmah]

and 'no'. The PWM always involves division. The fastest possible is 8MHz from
a 32Mhz clock, and with this you have just four different pulse widths.
To run a PWM at 32MHz, would be a very unusual requirement. Few drivers
would support the switching speeds needed for this. Typically even 500KHz
is 'unusually fast' for a PWM.

[ressas]

Thank you Temtronic and Ttelmah
You're right. I always ask. But I have to try it myself.
My English is weak. away from concepts.

As a Turkish proverb says;
To do someone a favor, teach him how to fish. Dont give a fish