Elapsed_Int-18 Alteration

[Rob]

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

' ------------------------------------------------------------------------------
' 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:

; -----------------  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

[Darrel Taylor]

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,

[Rob]

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

Cheers Darrel - much appreciated!

[Rob]

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:

</i></font>StartTimer:
    <b>IF </b>OSC = 48 <b>THEN              </b><font color="#000080"><i>; IF OSCILLATOR IS 48MHz THEN
        </i></font>@ BSF T1CON,T1CKPS0, 0    <font color="#000080"><i>; SET PRESCALE VALUE TO 2
    </i></font><b>ENDIF
    </b>T1CON.1 = 0                   <font color="#000080"><i>; (TMR1CS) Select FOSC/4 Clock Source
    </i></font>T1CON.3 = 0                   <font color="#000080"><i>; (T1OSCEN) Disable External Oscillator
    </i></font>T1CON.0 = 1                   <font color="#000080"><i>; (TMR1ON) Start TIMER1
</i></font><b>RETURN</b>

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!

[Darrel Taylor]

Try it like this ...

<font color="#000000"><b>StartTimer</b>:
<font color="#000080">@   IF OSC == 48                  </font><font color="#0000FF"><b><i>; IF OSCILLATOR IS 48MHz THEN
</i></b></font><font color="#000080">@       BSF T1CON,T1CKPS0, 0      </font><font color="#0000FF"><b><i>; SET PRESCALE VALUE TO 2
</i></b></font><font color="#000080">@   ENDIF
    </font><b>T1CON</b>.<font color="#800000"><b>1 </b></font>= <font color="#800000"><b>0                   </b></font><font color="#0000FF"><b><i>; (TMR1CS) Select FOSC/4 Clock Source
    </i></b></font><b>T1CON</b>.<font color="#800000"><b>3 </b></font>= <font color="#800000"><b>0                   </b></font><font color="#0000FF"><b><i>; (T1OSCEN) Disable External Oscillator
    </i></b></font><b>T1CON</b>.<font color="#800000"><b>0 </b></font>= <font color="#800000"><b>1                   </b></font><font color="#0000FF"><b><i>; (TMR1ON) Start TIMER1
</i></b></font><font color="#008000"><b>RETURN
</b></font>

The OSC value isn't directly available to PBP.

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

<font color="#000000"><b>PicOSC  </b><font color="#008000"><b>CON </b></font><b>EXT
</b><font color="#000080">@PicOSC = OSC

</font><b>StartTimer</b>:
    <font color="#008000"><b>IF </b></font><b>PicOSC </b>= <font color="#800000"><b>48 </b></font><font color="#008000"><b>THEN           </b></font><font color="#0000FF"><b><i>; IF OSCILLATOR IS 48MHz THEN
</i></b></font><font color="#000080">@       BSF T1CON,T1CKPS0, 0      </font><font color="#0000FF"><b><i>; SET PRESCALE VALUE TO 2
    </i></b></font><font color="#008000"><b>ENDIF
    </b></font><b>T1CON</b>.<font color="#800000"><b>1 </b></font>= <font color="#800000"><b>0                   </b></font><font color="#0000FF"><b><i>; (TMR1CS) Select FOSC/4 Clock Source
    </i></b></font><b>T1CON</b>.<font color="#800000"><b>3 </b></font>= <font color="#800000"><b>0                   </b></font><font color="#0000FF"><b><i>; (T1OSCEN) Disable External Oscillator
    </i></b></font><b>T1CON</b>.<font color="#800000"><b>0 </b></font>= <font color="#800000"><b>1                   </b></font><font color="#0000FF"><b><i>; (TMR1ON) Start TIMER1
</i></b></font><font color="#008000"><b>RETURN
</b></font>

[Rob]

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