HP-71B Tip
Joseph Horn  <53>
Brian Walsh  <1>


An HP-71 user called with a problem:  How do you recover a file recorded on a set of
cards when some of the cards have been recorded over?  The user is a surveyor who
wanted to recover a large data file.  Although a card reader may not be the most
efficient way to store data, its small size and weight make it convenient to use.  HP
said it would probably require and assembly language program to recover the data.  A
user skilled in HP-71 assembly language said it could be done but did not offer any
great encouragement.

Joe Horn came up with this idea:
1. COPY :CARD [ENDLINE]
2. After reading in all of the card tracks you have (even though the HP-71 still
prompts for the lowest track not read), do an INIT:1 by pressing ON and /
simultaneously.
3. The 71 will leave the file you tried to read in a very large file of File Type 0.
You will need to change the file to the proper type.
4. Using the address returned by ADDR$(filename) plus 16 nybbles, POKE the
appropriate 4 nybbles to change the file type.
     File type:     POKE data:
     DATA 0F0E
     SDATA     0D0E
     TEXT 1000
See the HP-71 Internal Design Specifications for other file types.
5. It is probably best to back up everything in your machine before trying this
procedure.

If you try this and find any errors, please let one of us know!

Joseph Horn  <53>
1042 Star Route
Orange, CA 92667

Brian Walsh  <1>