> I think so.  This is a lot more complicated to explain than to do, so here
> is a example.  This example will extend the capture timer to 24 bits, so
> the
> sofware accumulator will be 16 bits wide.  All numbers are in HEX:


Depending on the application, it might be simpler to just monitor the
change in the MSB of TMR1H:

; 24-bit software timer that shadows TMR1
;
; Copy TMR1H:L to the low 16 bits of the software timer.
; If TMR1 rolled over since the last update, then increment
; high byte of the software timer
;
;   Software timer
; SWTmrHigh  ; bits 23-16
; SWTmrMid   ; bits 15-8
; SWTmrLow   ; bits 7-0

    MOVF   TMR1L,W     ;Read the HW timer (latches TMR1H too)
    MOVWF  SWTmrLow

    INCF   SWTmrHigh,F ;Assume that there was a roll over

    BTFSS  TMR1H,7     ;If the MSB of the HW timer is set
     BTFSS SWTmrMid,7  ;or bit 15 of the SW timer is clear
      DECF SWTmrHigh,F ;then there was no roll over

    MOVF   TMR1H,W     ;Update the middle byte.
    MOVWF  SWTmrMid

This assumes that the software timer is updated at a rate faster then one
half of the period of time for a hardware timer roll over.

Note, this has not been tested!

Scott
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