You cannot assign the bit for the bit testing instructions at run time; it
is assigned and encoded into the instruction at compile time (i.e., when you
assembly your program).

However, you could write you routines in such a way that they used the AND
instruction. Then you can test for the Zero condition (Z flag = 1, the bit
was a zero, Z flag = 0, the bit was a one).

Douglas Wood
Software Engineer
dbwood@kc.rr.com
ICQ#: 143841506

Home of the EPICIS Development System for the PIC
http://epicis.piclist.com

----- Original Message -----
From: "Scott Pierce" <piclist@CALCLINKS.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, January 31, 2003 11:16 PM
Subject: Subroutines


> I have four inputs on PortA that I want to read pulse values from but not
> at the same time.  Say I have a subroutine to read PortA pin 0, grab the
> pulse length from it,  then return to the calling subroutine, then I want
> to use the same pulse reading subroutine to grab the pulse length on PortA
> pin 1 and so on.  Is there a way to do this or do I have to write a
> separate subroutine for each pin on PortA.  The reason I ask is because I
> am using BTFSC PORTA, PIN to wait until the pin goes low.  My
understanding
> of BTFSC is that the bit (PIN) value must be a literal and cannot be
stored
> in a register.  If I tried to use a register value it would take the
actual
> address of the register and try to use that instead of what is contained
in
> the register.  Do I understand that correctly?  Is there a trick to doing
> what I want to do?  Here is a snippet of my source code so you can get a
> better idea of what I'm trying to do.  As you will see, The four
> subroutines basically do the exact same thing with the exception of
reading
> a different pin on PortA and writing to one of four different
> registers.  This would not be a problem except this fills half of my
> program memory on my 16F84A and this code is only a third or so of the end
> program.  If there is no work around, should I just move to a PIC with
more
> program memory?  Thanks in advance.
>
> Sincerely,
> Scott Pierce
>
> <snippet>
>
> MAINLOOP        CALL    ROLL_PULSE
>                 CALL    PITCH_PULSE
>                 CALL    THROTTLE_PULSE
>                 CALL    YAW_PULSE
>
>                 GOTO    MAINLOOP
>
>
;===========================================================================
===
>
> ROLL_PULSE      CLRF    ROL                     ;CLEAR ROL COUNTER
> ROL2            BTFSC   PORTA,ROLP              ;LOOP UNTIL PORTA,ROLP PIN
IS CLEARED
>                 GOTO    ROL2
>
> ROL3            BTFSS   PORTA,ROLP              ;LOOP UNTIL PORTA,ROLP PIN
IS SET
>                 GOTO    ROL3
>
> ROL4            INCF    ROL                     ;INCREMENT ROL COUNTER
>                 CALL    PAUSE
>                 BTFSC   PORTA,ROLP              ;LOOP UNTIL PORTA,ROLP PIN
IS CLEARED
>                 GOTO    ROL4
>                 ;MOVF   ROL,W                   ;LOAD W WITH ROL
>                 ;MOVWF  PORTB           ;LOAD PORTB WITH VALUE OF ROL
>                 RETURN
>
>
;===========================================================================
===
>
> PITCH_PULSE     CLRF    PIT             ;CLEAR PIT COUNTER
> PIT2            BTFSC   PORTA,PITP              ;LOOP UNTIL PORTA,PITP PIN
IS CLEARED
>                 GOTO    PIT2
>
> PIT3            BTFSS   PORTA,PITP              ;LOOP UNTIL PORTA,PITP PIN
IS SET
>                 GOTO    PIT3
>
> PIT4            INCF    PIT                     ;INCREMENT PIT COUNTER
>                 CALL    PAUSE
>                 BTFSC   PORTA,PITP              ;LOOP UNTIL PORTA,PITP PIN
IS CLEARED
>                 GOTO    PIT4
>                 ;MOVF   PIT,W                   ;LOAD W WITH PIT
>                 ;MOVWF  PORTB           ;LOAD PORTB WITH VALUE OF PIT
>                 RETURN
>
>
;===========================================================================
===
>
> THROTTLE_PULSE  CLRF    THR             ;CLEAR THR COUNTER
> THR2            BTFSC   PORTA,THRP              ;LOOP UNTIL PORTA,THRP PIN
IS CLEARED
>                 GOTO    THR2
>
> THR3            BTFSS   PORTA,THRP              ;LOOP UNTIL PORTA,THRP PIN
IS SET
>                 GOTO    THR3
>
> THR4            INCF    THR                      ;INCREMENT THR COUNTER
>                 CALL    PAUSE
>                 BTFSC   PORTA,THRP              ;LOOP UNTIL PORTA,THRP PIN
IS CLEARED
>                 GOTO    THR4
>                 ;MOVF   THR,W                   ;LOAD W WITH THR
>                 ;MOVWF  PORTB           ;LOAD PORTB WITH VALUE OF THR
>                 RETURN
>
>
;===========================================================================
===
>
> YAW_PULSE       CLRF    YAW                     ;CLEAR YAW COUNTER
> YAW2            BTFSC   PORTA,YAWP              ;LOOP UNTIL PORTA,YAWP PIN
IS CLEARED
>                 GOTO    YAW2
>
> YAW3            BTFSS   PORTA,YAWP              ;LOOP UNTIL PORTA,YAWP PIN
IS SET
>                 GOTO    YAW3
>
> YAW4            INCF    YAW                     ;INCREMENT YAW COUNTER
>                 CALL    PAUSE
>                 BTFSC   PORTA,YAWP              ;LOOP UNTIL PORTA,YAWP PIN
IS CLEARED
>                 GOTO    YAW4
>                 ;MOVF   YAW,W           ;LOAD W WITH YAW
>                 ;MOVWF  PORTB           ;LOAD PORTB WITH VALUE OF YAW
>                 RETURN
>
>
;===========================================================================
===
>
> </snippet>
>
> --
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