Per my understanding, you do not have to enable the Global interupt if you set
INTCON <1>  to 1 (high).  However, to be for sure, I would enable the global
interupt (INTCON<7>) and turn off (set to 0) all other interupts you do not plan
to use. (Of course you will keep INTCON<1> high, because you are using it).

A book that I purchased is Programing and Customizing the Pic Microcontroller by
Myke Predko.  This is a descent beginners book.  My opinion is that the author
does not go into enough detail on some topics and does a really poor job of
guiding you to the sections of the book that would provide further information
(he tells you it is there and then you have to read the whole book to find it).
With that said, it seems to be one of the most popular books out there for
beginners.

Mathew Cohen wrote:

> Thanks John,
>
> I Believe it is blaintly obvious that I am a complete newby to this. Trying
> to run before I can walk.
> Can you also tell me weather I have to enable the global interupt bit before
> the timer overflow interupt will work.
>
> Thanks again
>
> Mathew Cohen
> mathew@everythingit.net
>
> ----- Original Message -----
> From: John Considine <jconsi@MAGICNET.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Wednesday, October 27, 1999 12:41 PM
> Subject: Re: Why doesn't this code work ???
>
> > The PIC16C84 has the interupt at org 4
> > I don't see you saving the registers after going into interupt and
> returning
> > the registers when returning (you should have a RETFIE, not a return)
> > _w    equ    10
> > _status    equ    11
> >
> > org 4
> > Interrupt
> > movwf    _w                ;save work
> > movf     STATUS, w
> > bcf        STATUS, RP0    ;puts the pic register in a know page (optional)
> > movwf    _status        ;save status
> >
> > bcf    INTCON, 1    ;clear INTF in INTCON register
> > bcf    INTCON, 2    ;ckear TOIF in INTCON register
> >
> > Do your other interupt code here
> >
> > RETFIE                    ;puts the PC at Top of Stack (where the interupt
> came
> > from)
> >
> >
> >
> >
> >
> > Mathew Cohen wrote:
> >
> > > I believe that this is the interupt vector location for the 16f84. In
> > > software simulation it seems to work. If this is not the case than could
> > > someone please set me straight. Also it ahs been brought to my attention
> > > that I seem to have left the global interupt bit low this is probably
> why
> > > the code does not work .
> > > Can someone test it thanks.
> > >
> > > Regards
> > >
> > > Mathew Cohen
> > >
> > > ----- Original Message -----
> > > From: Martin Schdfer <Schaefer@ELEKTRONIK21.DE>
> > > To: <PICLIST@MITVMA.MIT.EDU>
> > > Sent: Wednesday, October 20, 1999 10:21 PM
> > > Subject: Re: Why doesn't this code work ???
> > >
> > > > Hi Mathew,
> > > >
> > > > why is your interrupt starting at H'03' ?
> > > >
> > > > Mathew Cohen schrieb:
> > > >
> > > > >   Hi All, Can someone tell me why the following code will not work.
> Is
> > > > > this the correct way to initilise the timer and use the timer
> overflow
> > > > > interupt. Thanks in advance Mathew Cohen               ORG
> > > > > H'50' Start
> > > > >  Call Initporta
> > > > >  Call Initportb
> > > > >  Call Initmr
> > > > >  GOTO
> > > > > Checkswitch
> > >
> ;--------------------------------------------------------------------------
> > > > > ORG H'03'
> > > > > TmrInterupt  BTFSC PORTB,7
> > > > >  call Initmr
> > > > >  goto toggleleds Initmr
> > > > >  CLRF TMR0
> > > > >  BSF STATUS,RP0 ;select bank 1
> > > > >  CLRF OPTION_REG
> > > > >  MOVLW B'00000111'
> > > > >  IORWF OPTION_REG,1
> > > > >  BCF INTCON,T0IF
> > > > >  BSF INTCON,T0IE  RETURN
> > > > > Initporta  BSF STATUS,RP0
> > > > >  MOVLW 0
> > > > >  TRIS PORTA
> > > > >  BCF STATUS,RP0
> > > > >  MOVLW 31
> > > > >  MOVWF PORTA  RETURN Initportb  BSF STATUS,RP0
> > > > >  MOVLW H'FF'
> > > > >  MOVWF TRISB
> > > > >  BCF STATUS,RP0
> > > > >  RETURN Checkswitch
> > > > >  BTFSS PORTB,7
> > > > >  BSF PORTA,4
> > > > >  BTFSC PORTB,7
> > > > >  BCF PORTA,4
> > > > >  GOTO Checkswitch
> > > > > toggleleds
> > > > >
> > > > >  BTFSS PORTA,1
> > > > >  goto LedsOFF
> > > > >  BTFSC PORTA,1
> > > > >  goto Ledson
> > > > >
> > > > > Ledson  MOVLW 15
> > > > >  MOVWF PORTA
> > > > >  CALL Initmr
> > > > >  GOTO Checkswitch
> > > > > LedsOFF
> > > > >
> > > > >  MOVLW 0
> > > > >  MOVWF PORTA
> > > > >  CALL Initmr
> > > > >  GOTO Checkswitch
> > > > >
> > > > >  END
> > > >
> >