Triggering A/D conversion using PWM special event trigger

[Guest]

From reading the PIC18F1330 manual I can see that the PWM special event trigger can be used to start an a/d conversion by setting the ADCON0 register appropriately. However the CCS manual does not explain how you would go about doing this. Similarly the PIC's header file makes no mention of how you set up the A/D to be triggered by the special event trigger. I would be very grateful if someone could explain to me how I can achieve this.

[Guest]

After looking at the code in EX_POWER_PWM.c and the header file for the 18F2431 I can see that there is a function to trigger the ADC from the PWM - setup_adc(adc_when_ppwm). I need this exact function but for the 18F1330. It's in the manual but the header file does not have it included as a function. Is there anything I can do about this? Thanks

[Guest]

I have tried programming the ADCON0 register directly to enable the special event trigger using ADCON0 = 0b10001101 in main(), but the compiler gives an error saying undefined idenifier ADCON0. This is my first attempt at directly programming registers rather than using the built in functions so I'm not entirely sure how I go about doing this.

[Ttelmah]

For anything where you want to access the registers, you need to define them yourself (some exceptions like the timers).

However there is a 'caveat', in that you shouldn't trigger a reading, in the same operation as setting the config. Better to get the config set, then set the trigger afterwards.
Just do this:

[Guest]

Thank you for that info. So does #bit SEVTEN=0xFC2.7 define bit 7 of the ADCON0 register? If you could briefly explain that it would be great as I don't quite understand the syntax of directly accessing a register. Or point me in the direction of somewhere that explains this.
The program will also have other A/D conversions to carry out, but these should not be synchronised with the PWM. Can I do them normally by putting SEVTEN=FALSE; before calling the A/D function?

Kind Regards

[Ttelmah]

Read the manual.....

Two instructions. #bit, and #byte. The first defines a _bit_ variable, at a specific address and bit. The second defines a byte variable at a specific address (and can also be used to place larger variables at a specific location).

Yes.
You could turn of the special event trigger, then just call:
val=read_adc();

and this will trigger a conversion, wait for it to complete, and read the result.

Best Wishes

[Guest]

Thank you for your help, I think I'll be able to get it to work now. It's a shame that I have to manually/directly set the register when the exact function for it is present in the header file for many other PIC devices. It is something CCS must have forgotten to add for the 18F1330.

[Ken Johnson]

Also, look at getenv(), which saves you having to lookup the actual register address in the data sheet.

Examples:

#pragma BYTE TXREG1 = getenv("SFR:TXREG")

#pragma BIT RC1IE = getenv("BIT:RCIE")

Ken