Elapsed Timer findings

[Art]

Hi Guys,

I finally figured out how the constant timer values are calculated for various oscillator speeds in DT’s Elapsed Timer.

  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 == 20
TimerConst = 03CB7h
  EndIF

For the 20MHz example where the constant is 03B7h, it's the reverse of this:

FFFFh - 03B7h = C348h (49992 decimal),
49992 + 8 = 50000 (it must take eight instruction cycles to reload the timer)
50000 / 10000 = 5
5 x 4 = 20MHz

I was looking for this:

  If OSC == 16
TimerConst = 063C7h
  EndIF

Apologies if this info is already out there.
Cheers, Art.