----- Original Message -----
From: David V. Fansler <DFansler@MINDSPRING.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, December 11, 2002 3:12 PM
Subject: [PIC]:String Copy in ASM


> I am working on a project where I am receiving strings of data via RS-232.
> The data is NMEA sentences, of which I do not need all data from every
> sentence.  Therefore I am parsing the data as it is received and writing
the
> data into a buffer of on board RAM (16F873).  Once the entire sentence is
> received, I am copying data from the buffer and placing it in different
> locations from where it will be displayed.  Some of the sentences have a
> "data valid" flag, that often is not the first byte of data, so I need to
> place the data in temp storage until I am sure the data is valid.
>
> The problem I am currently addressing is copying string data from one
> location to another - in assembler.  Using direct addressing would make
the
> program way to large for the amount of program memory on the 16F873.
There
> are 35 pieces of data (from 1 byte to 10 bytes in length) in 24 sentences
> that can be up to 80 bytes long.  Therefore I am using indirect
addressing.
> The problem with indirect addressing is that, as I understand it, you can
> only be indirectly addressing one place at the time.  The method for
> handling this that I have come up with is to:
>
> 1 set up the FSR for the byte to be read
> 2 read the byte using INDF and store in a temp location - check for end of
> string - exit if EOS
> 3 inc the FSR and save into another temp location (FSR_READ)
> 4 load FSR with the register to write to (stored in FSR_WRITE)
> 5 read the byte from its temp location
> 6 write the byte using INDF
> 7 inc FSR and save FSR in FSR_WRITE
> 8 load FSR with the register to read from (FSR_READ)
> 9 loop back to #2
>
> Any one have a better idea, or has anyone done string copying in assembler
> before?  I searched the archives and did not find anything.  I want to use
> assembler - not C, and I wish to stay with the 16F87x series.
>
> Thanks,
> David
>
> David V. Fansler
> DFansler@MindSpring.com
> www.DV-Fansler.com
>

try using a small temporary buffer as follows
; j = pointer to source string
; k = pointer to destiniation string

lab1 movf j,w
 movwf FSR

 movf INDF,w
 incf FSR
 movwf tmp+0
 movf INDF,w
 incf FSR
 movwf tmp+1
 movf INDF,w
 incf FSR
 movwf tmp+2
 movf INDF,w
 incf FSR
 movwf tmp+3

; add more stages here if required

 movlw 4
 addwf j

 movf k,w
 movwf FSR

 movf tmp+0,w
 movwf INDF
 btfsc STATUS,Z
 goto lab99
 incf FSR
 movf tmp+1,w
 movwf INDF
 btfsc STATUS,Z
 goto lab99
 incf FSR
 movf tmp+2,w
 movwf INDF
 btfsc STATUS,Z
 goto lab99
 incf FSR
 movf tmp+3,w
 movwf INDF
 btfsc STATUS,Z
 goto lab99
 incf FSR

; add more stages here if required

 movlw 4
 addwf k

 goto lab1

lab99

Regards
Sergio Masci

http://www.xcprod.com

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