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

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