Timing on the 12F675

[abbtech]

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

[mackrackit]

You might try

GPIO = %xxxxxxxx

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

[Kamikaze47]

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

[Acetronics2]

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 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)

[sayzer]

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

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

[Bruce]

Something like this is easier with PBP.

This is in an include file;

  ' 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;

@ #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.

[Mike, K8LH]

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

[abbtech]

Thanks for all the help and suggestions.

Bruce, I tried your suggestion and it works great!

Regards,

Alan Parekh