I'm using timer1 to divide the instruction clock and keep time.  The 
problem that I am having is that I cannot seem to get 16 bit resolution out 
of the counter.

I set up the TMR1H and TMR1L to count clock cycles and to roll over after 
100mS.

I was close and wanted to adjust the value and found that I was unable to 
get the resolution that 16 bits should provide.

Clock = 4MHz
Fosc/4 = 1MHz
Prescale = 1:8
T1CON = %00110001

I calculate that I should have 8uS per count with this setup.
65536 counts will give an timer overflow at 0.524288 seconds.
I set up TMR1H and TMR1L with 0, 0 and that was the time that it took to 
fill the counter.  So far so good.

I then programmed the registers with
TMR1H = 207, TMR1L = 44 (16 bit: 53036) , the overflow occurred at 
102.4mS   (2.4ms too long)  I figured, OK I know I have to account for 
instruction time in resetting the timers, but 2.4mS?  That's approx. 2400 
instructions, so something else is going on here.

Next step was to program TMR1H and TMR1L up and down with values so that I 
could "dial in" the 100mS that I was looking for.

I adjusted the values up and nothing happened until I got to TMR1H = 209, 
TMR1L = 196 (16bit: 53700), at that point the interval decreased to 94.5mS

I adjusted the values down to get the transition point below 102.4mS and at 
TMR1H = 205, TMR1L = 236 (16 bit: 52716) the interval increased to 110.3 mS

So I have a count delta of 53700 - 52716 = 984 counts
My time delta between the two points is 102.4mS - 94.5mS = 15.8mS
That works out to about 16uS per count.  The problem is that the minimum 
change I can effect is 8mS increments and it takes 500 counts to do 
that.  So much for the 8uS increments.

I have included the update code below that I'm using to reset the timer for 
this test.

Any ideas what I'm doing wrong???

Thanks

Scott

-----------------------------------------------------
oscH and oscL are bank0 bytes and loaded outside of the loop

LoopStart
	clrf 	STATUS		;set to bank 0
   	btfss 	PIR1, 0			;test the TMR1IF
   	GoTo 	skipReset		; bit clear then skip the code
   	movf 	oscH, W		;get the high byte
   	movwf 	TMR1H			;save the high byte
   	movf 	oscL, W		;get the low byte
   	movwf 	TMR1L      		; finish reset of timer1
   	movlw 	4
   	xorwf 	PORTB, 1     		;TOGGLE LED
  	bcf  	PIR1, 0			;clear TMR1IF
skipReset
   	nop
	goto LoopStart





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