Now my code compiles fine thankyou, barring a overwriting previous address warning from my config settings (I understand why that is). But I have a small question regarding reloading the timer for anyone.

Must I stop the timer while reloading it with a hex value of A823 in the interrupt handler code (which is all it needs to do) ?

T1CON = %0
TMR1H = $A8
TMR1L = $23
T1CON = %1

Or can I ignore the stop-start safely. Given I can tweak the timer value by trial and error to get my 22.5mS @ 4Mhz ?

The only examples I've dug out on the forum are using ASM code and I'm not strong on interpreting it.