----- Original Message -----
From: Drew Vassallo <snurple@HOTMAIL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, January 04, 2001 10:45 PM
Subject: Re: [PIC]: Not use the address but what is inside that address


> The original problem was:
>
> > >     Petra: I should use any port, and any bit... my idea is to make a
> > > subrutine to read a bit using sofware filter...
>
> How is the routine below solving this problem?  It looks useful for
DEFINING
> a bit to output, not reading a bit in.

Oops, sorry -- lost track of the original request. Here is the code to check
a bit:

; To test bit "BitNum" or port "PortNum"

    movf    PortNum,W
    movwf FSR
    movf    BitNum,W
    call       BitToMask
    andwf  INDF,W

; At this point Z is set if PortNum,BitNum was clear
;  Z is clear if PortNum,BitNum was set

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)


> >You need to map from a bit number to a bitmask, then use logical
> >instructions:
> >
> >To turn on bit "BitNum" of port "PortNum":
> >
> >     movf       PortNum,W
> >     movwf    FSR
> >
> >     movf       BitNum,W
> >     call         BitToMask
> >     iorwf       INDF,F
> >
> >To turn off bit "BitNum" of port "PortNum":
> >
> >     movf       PortNum,W
> >     movwf    FSR
> >
> >     movf       BitNum,W
> >     call          BitToMask
> >     xorlw       0xFF
> >     andwf      INDF,F
> >
> >
> >BitToMask:
> >     addwf    pcl
> >     retlw    1
> >     retlw    2
> >     retlw    4
> >     retlw    8
> >     retlw    16
> >     retlw    32
> >     retlw    64
> >     retlw    128

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