Elapsed_Int-18 Alteration

I've added a slight alteration to Darrel's Elapsed_Int-18 to get 48MHz oscillator. Could somebody please check if this is correct?

Code:

' ------------------------------------------------------------------------------ ' To calculate a constant for a different crystal frequency - see this web page ' http://www.picbasic.co.uk/forum/showthread.php?t=2031 ' ------------------------------------------------------------------------------ Asm IF OSC == 4 ; Constants for 100hz interrupt from Timer1 TimerConst = 0D8F7h ; Executed at compile time only EndIF If OSC == 8 TimerConst = 0B1E7h EndIF If OSC == 10 TimerConst = 09E5Fh EndIF If OSC == 16 TimerConst = 063C7h EndIF If OSC == 20 TimerConst = 03CB7h EndIF If OSC == 48 ; If an oscillator of 48MHz is used e.g. TimerConst = 015A4h ; in USB PICs, set TimerConst to 015A4h. BSF T1CON,T1CKPS0, 0 ; MUST also set to prescale of 2 NOT 1 EndIF ; ----------------- ADD TimerConst to TMR1H:TMR1L ADD2_TIMER macro ; CHK?RP T1CON BCF T1CON,TMR1ON, 0 ; Turn off timer MOVLW LOW(TimerConst) ; 1 ADDWF TMR1L,F, 0 ; 1 ; reload timer with correct value BTFSC STATUS,C ; 1/2 INCF TMR1H,F, 0 ; 1 MOVLW HIGH(TimerConst) ; 1 ADDWF TMR1H,F, 0 ; 1 endm

The timer seems to run doubly quick like the prescale setting is not being set correctly. If I set the prescale setting in the ADD2_TIMER macro though it works correctly but will increase the amount of instructions required therefore altering the amount of time a tick takes:

Code:

; ----------------- ADD TimerConst to TMR1H:TMR1L ADD2_TIMER macro ; CHK?RP T1CON BCF T1CON,TMR1ON, 0 ; Turn off timer If OSC == 48 ; IF OSCILLATOR IS 48MHz THEN BSF T1CON,T1CKPS0, 0 ; SET PRESCALE VALUE TO 2 EndIF MOVLW LOW(TimerConst) ; 1 ADDWF TMR1L,F, 0 ; 1 ; reload timer with correct value BTFSC STATUS,C ; 1/2 INCF TMR1H,F, 0 ; 1 MOVLW HIGH(TimerConst) ; 1 ADDWF TMR1H,F, 0 ; 1 endm

Thanks in advance

Rob

Hi Rob,

The part that selects the Timer reload value only happens at compile time.
The BSF intruction never get's executed at run-time.

The best place to put it will be in the StartTimer: routine.

hth,

Massive thanks

Ahhhh, you know when the penny drops... I just had one of those moments!

Cheers Darrel - much appreciated!

Hmmm,

although I said the penny had dropped, I don't seem to be able to make the code work where you said to put it:

Code:

StartTimer: IF OSC = 48 THEN ; IF OSCILLATOR IS 48MHz THEN @ BSF T1CON,T1CKPS0, 0 ; SET PRESCALE VALUE TO 2 ENDIF T1CON.1 = 0 ; (TMR1CS) Select FOSC/4 Clock Source T1CON.3 = 0 ; (T1OSCEN) Disable External Oscillator T1CON.0 = 1 ; (TMR1ON) Start TIMER1 RETURN

Now when I compile my program, it comes up with the error: Bad expression or missing THEN. (Elapsed_INT-18.bas)

Is this because the oscillator has been defined in my program and not in the Elapsed_INT-18? I've had problems similar to this before when I've tried to create simple modules like you do (not saying that yours are simple I mean my ones!). I like that style of programming I just can't seem to make it work.

Thanks for any help.

Rob

P.s. I looked up your thread "Show us your colours"... I like it!

Try it like this ...

Code:

StartTimer: @ IF OSC == 48 ; IF OSCILLATOR IS 48MHz THEN @ BSF T1CON,T1CKPS0, 0 ; SET PRESCALE VALUE TO 2 @ ENDIF T1CON.1 = 0 ; (TMR1CS) Select FOSC/4 Clock Source T1CON.3 = 0 ; (T1OSCEN) Disable External Oscillator T1CON.0 = 1 ; (TMR1ON) Start TIMER1 RETURN 

The OSC value isn't directly available to PBP.

Or, you could make it available, and do it that way...

Code:

PicOSC CON EXT @PicOSC = OSC StartTimer: IF PicOSC = 48 THEN ; IF OSCILLATOR IS 48MHz THEN @ BSF T1CON,T1CKPS0, 0 ; SET PRESCALE VALUE TO 2 ENDIF T1CON.1 = 0 ; (TMR1CS) Select FOSC/4 Clock Source T1CON.3 = 0 ; (T1OSCEN) Disable External Oscillator T1CON.0 = 1 ; (TMR1ON) Start TIMER1 RETURN

All sorted!

Cool - it's working now! Cheers for showing me the second way as well as I think it may help me out with writing modules like you do!

Thanks very much

Rob