inaccurate frequency using TMR1 PI18F452

[nkarpovich]

1. I'm only showing part of the code, not all of it.
2. I'm not concerned about obtaining a frequency lower than it should be, I'm rather concerned about the gaps in frequency when changing by 1 the value I load into TMR1...
3. While the program is waiting for the interrupt it is only executing a while ...wend loop checking for two digital inputs, that's all. I presume the interrupt doesn't take that much in this case (no PAUSE instructions nor LCDOUT...)
4. When I add the ticks until interrupt routine executes the output frequency seems to be more unstable!!!!

suggestions are welcome, thanks a lot.

[Darrel Taylor]

>> 4. When I add the ticks until interrupt routine executes the output frequency seems to be more unstable!!!!

That shouldn't be the case. Can you show the code for how you're adding it into the timer value?
<br>

[nkarpovich]

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

[Darrel Taylor]

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...

@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
--------------------------------------------------------------------------------

[sayzer]

Let me edit a small part.

@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
--------------------------------------------------------------------------------

[nkarpovich]

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.

[mister_e]

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