How to set HPWM to generate 38khz signal? (16F870)

[CuriousOne]

Hello.

I'm building custom IR control, I already wrote the code for ir command generation, but I want to use built in hardwre pwm of 16F870 chip to generate 38khz carrier. PBP supports up to 32khz. Also, I'd be very grateful, if some gives me ASM code insert which simply enables and disables hpwm with already set frequency and duty cycle. The PBP command HPWM does too many things together, like switching port and so on, so it is slow.

[mackrackit]

http://www.picbasic.co.uk/forum/cont...ikon-IR-Remote

[CuriousOne]

Thanks, so I need this part of code, right?

ASM
_Pulse38
   bcf IRTX,PIN         ; 1uS, LED=on
   goto $+1             ; + 2uS = 3uS
   goto $+1             ; + 2uS = 5uS
   goto $+1             ; + 2uS = 7uS
   goto $+1             ; + 2uS = 9uS
   goto $+1             ; + 2uS = 11uS
   goto $+1             ; + 2uS = 13uS   
   bsf IRTX,PIN         ; 1uS, LED=on
   goto $+1             ; + 2uS = 3uS
   goto $+1             ; + 2uS = 5uS
   goto $+1             ; + 2uS = 7uS
   goto $+1             ; + 2uS = 9uS
   nop                  ; + 1uS = 10uS
   decfsz _Cycles,f     ; + 1uS = 11S    
   goto _Pulse38        ; + 2uS = 13uS
   return               ; Return to caller    
ENDASM

[CuriousOne]

and by the way, this code does nothing to built-in HPWM, right?

[HenrikOlsson]

No need for assembly code.
You want a PWM period of 1/38000 = 26.315us. Assuming 20MHz operating frequency your instruction cycle time is 200ns so you want a PWM period of 131-132 instruction cycles. Then you simply follow the instructions in the datasheet:

8.4.3 SETUP FOR PWM OPERATION
The following steps should be taken when configuring
the CCP module for PWM operation:
1. Set the PWM period by writing to the PR2 register.
2. Set the PWM duty cycle by writing to the CCPR1L register and CCP1CON<5:4> bits.
3. Make the CCP1 pin an output by clearing the TRISC<2> bit.
4. Set the TMR2 prescale value and enable Timer2 by writing to T2CON.
5. Configure the CCP1 module for PWM operation.

PR2 = 130                      ' 1) PWM period of 131 instruction cycles assuming 1:1 prescaler
CCPR1L = 65                  ' 2) Dutycycle of ~50%, no need to write 2 LSB for this.
TRISC.2 = 0                   ' 3) Pin is output
T2CON = %00000100      ' 4) 1:1 Prescaler, TMR2 ON
CCP1CON = %00001100    ' 5) PWM mode enabled

This sets up the carrier and enables it. To disable the carrier:

CCP1CON = 0

Enable it again:

CCP1CON = 15

I'm not 100% sure what the note in the datasheet says

Note: Clearing the CCP1CON register will force
the CCP1 PWM output latch to the default
low level. This is not the PORTC I/O data
latch.

It either says that as long as you set PortC.2 to 0 the output pin will revert to 0 as soon as the CCP module is disabled (which is good in this case) OR it says that actual output pin is left in the state it was at the time the CCP module was disabled which means that it can be high or low and that you need to force it back down by doing PortC.2 = 0 after turning off the CCP module.
(Untested, please verify against datasheet)

/Henrik.

[mackrackit]

And this tells how to pass data.
https://web.archive.org/web/20120307...B_PIC_TEMP.htm