Thanks for the advice, I tried it and traced the problem back to the 555.
Boosting the voltage on the 555 to 6V solved the problem

Thanks
Stephan
----- Original Message -----
From: Jan Erik Bertram <xirxe@GMX.DE>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, December 18, 1999 3:37 AM
Subject: Re: TMR1 Problem on 16c74a


> Perhaps you should connect RC0 with RC1 and then change your program a
bit.
>
> loop1
>      bcf    PORTC,1
>      bsf    PORTC,1
>      btfss PIR1,0  ; check if done
>      goto loop1  ; no, wait
>      return   ; done
>
> If this don't run then you have a problem with the pic, else it's a
problem
> with your 555.
>
> Ciao
>     Jan Erik Bertram
>
> ----- Original Message -----
> From: "Stephan Kotze" <stephank@IAFRICA.COM>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Friday, December 17, 1999 8:13 PM
> Subject: TMR1 Problem on 16c74a
>
>
> Dear list
>
> I have been running into a strange problem on the 16c74a. I am trying to
use
> tmr1 as a state machine clock but it won't for the life of me work. I
> include the relevant code snippets
>      bsf STATUS,RP0  ; Page 1 of registers
>     clrf TRISD            ;
>     clrf TRISE            ; Ports D and E all outputs
>      movlw 0x9b              ; all bits are outputs except RC0,SDI,sck &
RX
>      movwf TRISC             ; do it
>     bcf STATUS,RP0    ; Back to page 0
> initTMR1
>      clrf TMR1L
>      clrf TMR1H    ;clear high and low registers
>      MOVLW B'00000110' ;
>      MOVWF T1CON   ; Enable T1 Oscillator, Ext Clock, Async, prescaler = 1
>      BSF T1CON, TMR1ON  ; Turn Timer1 ON
>
> to initialise and then
>
> cycle
>         movlw 0x02
>         call Timer_wait
>          comf PORTE,f ; cycle portE
>          comf PORTD,f    ; Cycle port D
>          goto cycle ;
> Timer_wait ; number of cycles to wait in W
>      bcf T1CON,0  ;stop timer
>      movwf TMR1L ; put in low byte
>      comf TMR1L,f ; compliment to count up
>      bcf PIR1,0  ; clear overflow flag
>      movlw 0xff  ; put in W
>      movwf TMR1H  ; high byte
>      bsf T1CON,0  ; start timer again
> loop1
>      btfss PIR1,0  ; check if done
>      goto loop1  ; no, wait
>      return   ; done
>
> The clock signal on RC0 is a slow (20ms) pulse from a 555. Removing the
> "call Timer_wait" instruction cycles the ports perfectly at clock rate.
Also
> running the code in MPSIM works perfectly.
>
> Please help!!!!
>
> Stephan