Timing on the 12F675

I am using PicBasic Pro with the 12F675. I am using the internal 4MHz oscillator and seem to be having some issues.

I will need to create 30KHz, 33KHz, 36KHz, 38KHz, 40KHz and 56KHz. 38KHz is the most important and the one that I am working with first. I would like to make a 13uS on and 13uS off square wave.

If I run just a tight loop turning the output on and off the output is about 4.4uS on and 4.4uS off. Does this sound correct?

I tried to use pauseus 13 thinking that I would get a 13uS pause but it created about a 25uS pause. pauseus 1 still causes a 25uS pause. Is there that much overhead in turning the pin high and low.

Here is what I am trying.

freq38K:
HIGH IrLed
PAUSEUS 13
LOW IrLed
PAUSEUS 13
GOTO freq38k

You might try

Code:

---

GPIO = %xxxxxxxx

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Make the x's 0 or 1. 1 being high.

If the frequency needs to be accurate you would be much better off using a timer interrupt.

Hi,

as the Holy Manual states ...

min PAUSEUS @ 4 Mhz is ... 19µs ...

soooo .... toobad !

Now, for this " universal IR Tx " ...the use of a Xtal looks compulsory !

Alain

PS: an assembler stubb would be useful here ...

Code:

---

;-------------------------------------------------------------
; Code generated by PDEL  ver 1.0  on 23/04/2010 at 09:01:45
; Description: Waits 13 cycles
;-------------------------------------------------------------
PDelay  movlw    .2        ; 1 set number of repetitions
        movwf    PDel0    ; 1 |
PLoop0  clrwdt              ; 1 clear watchdog
        decfsz    PDel0, 1  ; 1 + (1) is the time over?
        goto      PLoop0    ; 2 no, loop
        return              ; 2+2 Done
;-------------------------------------------------------------



Code requirements
-----------------
- Declaration of PDel0 (register)
- 1 stack level

Example of use
--------------
call PDelay      ; Delay 13 cycles (including call+return)

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http://www.rentron.com/Infrared_Communication.htm

Code:

---

PROCESSOR 12c508
  #include "p12c508.inc"
  __CONFIG  _MCLRE_OFF & _CP_OFF & _WDT_OFF & _IntRC_OSC
  #DEFINE PORT B'11111101'
        MOVF OSCCAL
        MOVLW PORT
        TRIS GPIO
               
  BEGIN
        BCF GPIO, 1    ;1uS
        NOP                ;2uS each nop is 1uS long
        NOP                ;3uS
        NOP                ;4uS
        NOP                ;5uS
        NOP                ;6uS
        NOP                ;7uS
        NOP                ;8uS
        NOP                ;9uS
        NOP                ;10uS
        NOP                ;11uS
        NOP                ;12uS
        NOP                ;13uS
        NOP                ;14uS
        NOP                ;15uS
        NOP                ;16uS
        NOP                ;17uS
        NOP                ;18uS
        NOP                ;19uS
        BSF GPIO, 1        ;1uS Begin HIGH duty cycle
        NOP                ;2uS
        NOP                ;3uS
        NOP                ;4uS
        NOP                ;5uS
        GOTO BEGIN      ;2uS (26uS total for 38KHz)
        END

---

Something like this is easier with PBP.

This is in an include file;

Code:

---

  ' IR carrier generator routines. Freq.inc.

  Cycles VAR BYTE    ' Number of carrier cycles
 
  GOTO OverFreq  ' jump over pulse routines
 
' Generate "Cycles" number of 40kHz pulses
ASM
_Pulse40
  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
  decfsz _Cycles,f ; + 1uS = 10S   
  goto _Pulse40    ; + 2uS = 12uS
  return          ; Return to caller   
ENDASM

' Generate "Cycles" number of ~38.4kHz pulses
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

OverFreq:

---

Create one for whatever IR carrier freq you need, and just call them like this with PBP;

Code:

---

@ #define IRTX GPIO  ; Define port to use for IR out
@ #define PIN 2      ; Define port pin to use for IR out

INCLUDE "Freq.inc" '

  GPIO.2 = 1      ' IR LED off  -----|<|----/\/\/\----+5
  TRISIO.2 = 0    ' Output for IR signal
  CMCON = 7        ' Comparators disabled
  ANSEL = 0        ' A/D disabled
     
Main:
  Cycles = 60      ' min 1, max 255
  CALL Pulse38
  GOTO Main
 
  END

---

At 4MHz you won't be spot-on for every carrier frequency, but it will be close enough to work with pretty much any off-the-shelf IR receiver.

Have you considered using an 8-pin 12F683 and generating a 38-KHz PWM signal output in the background? Use a interval counter and turn the PWM output on or off at the correct intervals by setting the CCPR1L duty cycle register to 50% or 0%.

Regards, Mike

Thanks for all the help and suggestions.

Bruce, I tried your suggestion and it works great!

Regards,

Alan Parekh