PORTA register won't bit set (MPLAB)

When I execute my simple program in MPLAB the PORTA filer register bit 0 is 
not being set, but I can easily set bit 0 of the FSR register that sits 
right next to PORTA in the micro. In fact, nothing I do to PORTA works. Has 
anyone seen this before?

Start     BSF STATUS, RP0
            MOVLW B'11111110'
            BCF STATUS, RP0

            BSF PORTA, 0     ;doesn't work
            BSF FSR, 0           ;works

Thanks,
Thomas 

On Nov 22, 7:48=A0pm, "Thomas Magma" <somewh...@overtherainbow.com>
wrote:
> When I execute my simple program in MPLAB the PORTA filer register bit 0 =
is
> not being set, but I can easily set bit 0 of the FSR register that sits
> right next to PORTA in the micro. In fact, nothing I do to PORTA works. H=
as
> anyone seen this before?
>
> Start =A0 =A0 BSF STATUS, RP0
> =A0 =A0 =A0 =A0 =A0 =A0 MOVLW B'11111110'
> =A0 =A0 =A0 =A0 =A0 =A0 BCF STATUS, RP0
>
> =A0 =A0 =A0 =A0 =A0 =A0 BSF PORTA, 0 =A0 =A0 ;doesn't work
> =A0 =A0 =A0 =A0 =A0 =A0 BSF FSR, 0 =A0 =A0 =A0 =A0 =A0 ;works
>
> Thanks,
> Thomas

porta is analoge by default, you need to set it to digital.

Thomas Magma wrote:
> When I execute my simple program in MPLAB the PORTA filer register bit 0 is 
> not being set, but I can easily set bit 0 of the FSR register that sits 
> right next to PORTA in the micro. In fact, nothing I do to PORTA works. Has 
> anyone seen this before?
> 
> Start     BSF STATUS, RP0
>             MOVLW B'11111110'
>             BCF STATUS, RP0
> 
>             BSF PORTA, 0     ;doesn't work
>             BSF FSR, 0           ;works
> 
> Thanks,
> Thomas 

What is the purpose of the first three lines? And why do you change RP0 
before and after the MOVLW? Doesn't make sense...

Maybe you meant to do this:

START   BSF     STATUS,RP0
         MOVLW	B'11111110'
	MOVWF	TRISA
         BCF     STATUS,RP0

         BSF     PORTA,0
         ...

Some PICs have analogue inputs (for comparator/ADC modules) multiplexed 
with port A, in which case you need to disable these modules to use port 
A for general I/O. See the PIC's data sheet.

-- 
Regards,
Costas
_________________________________________________
Costas Vlachos  Email: c-X-vlachos@hot-X-mail.com
SPAM-TRAPPED: Please remove "-X-" before replying

<cbarn24050@aol.com> wrote in message 
news:1164225410.622053.308300@j44g2000cwa.googlegroups.com...


On Nov 22, 7:48pm, "Thomas Magma" <somewh...@overtherainbow.com>
wrote:
> When I execute my simple program in MPLAB the PORTA filer register bit 0 
> is
> not being set, but I can easily set bit 0 of the FSR register that sits
> right next to PORTA in the micro. In fact, nothing I do to PORTA works. 
> Has
> anyone seen this before?
>
> Start   BSF STATUS, RP0
>       MOVLW B'11111110'
>       BCF STATUS, RP0
>
>       BSF PORTA, 0   ;doesn't work
>       BSF FSR, 0      ;works
>
> Thanks,
> Thomas

porta is analoge by default, you need to set it to digital.

Thanks! That was it.

Thomas Magma <somewhere@overtherainbow.com> wrote in message
news:sm29h.345126$1T2.95425@pd7urf2no...
>
> >
> > Start   BSF STATUS, RP0
> >       MOVLW B'11111110'
> >       BCF STATUS, RP0
> >
> >       BSF PORTA, 0   ;doesn't work
> >       BSF FSR, 0      ;works
> >

Hi Thomas,

Also ideally you need to be writing to LATB instead of PORTB.  Of course you
*can* write to PORTB but it's a bad practice to get into.  It can create
headaches and quite mysterious behaviour as you become more advanced.

Remember..  Writes to the latch, Reads from the port.

There's alot of information regarding this topic;
http://forum.microchip.com/tm.aspx?m=193612  Lots of good info on the
Microchip Forum too.  Be concise with them on there because if you give the
impression that you're not trying at all or haven't read the manual, well,
you'll get the hang on it.  :)

Good luck :)

Is RP1 = 0? PortA is only in bank 0 and you may be switching between banks 2 
and 3 with your code.

Mike.

"Thomas Magma" <somewhere@overtherainbow.com> wrote in message 
news:qQ19h.345033$1T2.48459@pd7urf2no...
> When I execute my simple program in MPLAB the PORTA filer register bit 0 
> is not being set, but I can easily set bit 0 of the FSR register that sits 
> right next to PORTA in the micro. In fact, nothing I do to PORTA works. 
> Has anyone seen this before?
>
> Start     BSF STATUS, RP0
>            MOVLW B'11111110'
>            BCF STATUS, RP0
>
>            BSF PORTA, 0     ;doesn't work
>            BSF FSR, 0           ;works
>
> Thanks,
> Thomas
>