Changing PreScaler during interrupt

[bcd]

I am using a F737 which shares the pre-scaler between the Watchdog and TMR0.

Re-reading the data sheet I can see where I was getting a bit confused <code>(From the datasheet)
When assigned to the Timer0 module, all instructions
writing to the TMR0 register (e.g., CLRF 1, MOVWF 1,
BSF 1,x....etc.) will clear the prescaler. When assigned
to WDT, a CLRWDT instruction will clear the prescaler
along with the Watchdog Timer.
The prescaler is not
readable or writable.
</code>

I was thinking Pre-Scaler meant the ratio rather than the count. Looks like it should work. Might be time to break out the breadboard and see what happens...

bill

[skimask]

I am using a F737 which shares the pre-scaler between the Watchdog and TMR0.....................
I was thinking Pre-Scaler meant the ratio rather than the count. Looks like it should work. Might be time to break out the breadboard and see what happens...
bill

Yep, same deal with the 18F4620, and probably most other PICs. I think you got the picture.

[bcd]

Its a bit messy - but it works ! Tomorrow we optimise !
This is a snippet that shows how to change the Prescaler value from within the interrupt routinue using Instant Interrupts.

DEFINE OSC 20

rs_led      var portb.7
led          var portc.4 

loops       var byte    ' count round the loop to load prescaler


INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts


ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR0_INT,  _doBAM,   PBP,  yes
    endm
    INT_CREATE     ; Creates the interrupt processor
ENDASM

OPTION_REG = %11010000 'Set TMR0 Prescaler to 2, leave RBPU alone

TMR0 =  158 ' preload with 158 to give 21uS interrupts
loops = 0

' interrupt routinue
doBAM:
toggle rs_led
if loops > 6 then 
loops = 0
else
loops = loops+1
endif
option_reg.0 = loops.0
option_reg.1 = loops.1
option_reg.2 = loops.2
TMR0 =  158
@ INT_RETURN

bill.