inaccurate frequency using TMR1 PI18F452

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  1. - 13th October 2006, 23:09 #1
    nkarpovich's Avatar
    nkarpovich
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    Default Interrupt routine

    Code:
    Disable  
miint:
	IF PIR1.0 = 1 THEN
		T1CON.0 = 0
		OFFCNT_H =TMR1H
		OFFCNT_L =TMR1L
		IF ARRANCA_MOTOR = 1 THEN
			PORTC.5 = 0				'PULSO DE STEP
			PORTA.5 = 0					'SALIDA PARA SHAFT
			PRESCALER = FRECUENCIA + OFFCNT
			TMR1H = PRESCALERH
			TMR1L = PRESCALERL
			PORTA.5 = 1				'SALIDA PARA SHAFT
			PORTC.5 = 1				'PULSO DE STEP
		ELSE
			IF EMULACION = 1 THEN
				IF ACTIVA_PRESENCIA = 0 THEN
					TRIGGER = 0
				ELSE
					TRIGGER = 1
				ENDIF
			ENDIF
		ENDIF
	'*****************************************************************************************************
	ENDIF
	T1CON.0 = 1
	PIR1.0 = 0
	'**************************** INTERRUPCION POR TIMER 0  ****************************
	
salida1:
	Resume                 ' retorna al programa principal
 	Enable
    Last edited by Darrel Taylor; - 13th October 2006 at 23:18. Reason: added [code][/code] tags
  2. - 13th October 2006, 23:41 #2
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    Darrel Taylor
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    Default

    You always want the timer to reload the same on each interrupt. By placing it inside IF/THEN statements, it can change depending on the conditions.

    It also needs to be reloaded and re-started as soon as possible. Putting lot's of statements in-between turning the timer off and then back on again put's a variable amount of time in there as well.

    Try it this way...
    Code:
    @Timer1 = TMR1L
Timer1  VAR  WORD EXT

Disable  
miint:
	IF PIR1.0 = 1 THEN
		T1CON.0 = 0
		Timer1 = Timer1 + FRECUENCIA
		T1CON.0 = 1

		IF ARRANCA_MOTOR = 1 THEN
			PORTC.5 = 0				'PULSO DE STEP
			PORTA.5 = 0				'SALIDA PARA SHAFT
			PORTA.5 = 1				'SALIDA PARA SHAFT
			PORTC.5 = 1				'PULSO DE STEP
		ELSE
			IF EMULACION = 1 THEN
				IF ACTIVA_PRESENCIA = 0 THEN
					TRIGGER = 0
				ELSE
					TRIGGER = 1
				ENDIF
			ENDIF
		ENDIF
	'*****************************************************************************************************
	    PIR1.0 = 0
	ENDIF
	'**************************** INTERRUPCION POR TIMER 0  ****************************
	
salida1:
	Resume                 ' retorna al programa principal
 	Enable
--------------------------------------------------------------------------------
    DT
  3. - 14th October 2006, 04:45 #3
    sayzer's Avatar
    sayzer
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    Default

    Let me edit a small part.


    Code:
    @Timer1 = TMR1L
Timer1  VAR  WORD EXT

Disable  
miint:
	IF PIR1.0 = 1 THEN
		T1CON.0 = 0
		Timer1 = Timer1 + FRECUENCIA
		T1CON.0 = 1

		IF ARRANCA_MOTOR = 1 THEN
			PORTC.5 = 0	'PULSO DE STEP
			PORTA.5 = 0	'SALIDA PARA SHAFT
			PORTA.5 = 1	'SALIDA PARA SHAFT
			PORTC.5 = 1	'PULSO DE STEP
		ELSE
			IF EMULACION = 1 THEN TRIGGER = ACTIVA_PRESENCIA 

		ENDIF
	'*********************************************************
	PIR1.0 = 0
	ENDIF
	'**************** INTERRUPCION POR TIMER 0  **************
	
salida1:
	Resume                 ' retorna al programa principal
 	Enable
--------------------------------------------------------------------------------
    Last edited by sayzer; - 14th October 2006 at 04:48.
    "If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
  4. - 14th October 2006, 13:51 #4
    nkarpovich's Avatar
    nkarpovich
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    Default Pic18f452

    I've introduced the changes you suggested.
    I'm VERY pleased to find that frequency is no longer a function of the interrupt routine duration!
    Frequency output is still unstable and is constantly fluctuating end to end about 150 Hz when I set TMR1 to 65200 (7.3 KHz range). How can I improve frequency stability?
    Thanks a lot.
  5. - 14th October 2006, 17:22 #5
    mister_e's Avatar
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    Default

    Use an assembler ISR or use 'Instant interrupts' by Mr Darrel Taylor. REALLY NICE STUFF!
    http://www.pbpgroup.com/modules/wfse...p?articleid=19
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.
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