HOW TO RECOVER FROM A COLD START

Why is it that my NEC 8201A never locks up unless I have some text files in
RAM that have not been backed up?  After a few months without a hitch on
this old workhorse, I tend to forget that on rare occasions everything
in memory can suddenly disappear.   Usually, it happens when I'm using
someone's machine language utility program and end up out in never-never
land.  Returning to normal operations usually requires a cold start.
After that, of course, the Menu is empty and files are gone--or are they?

As long as the internal batteries are working, the 8201A retains its RAM
memory.  If the cold-start procedure (or the problem that caused it) did
not zap the entire RAM area, it would seem that some data should still
be there.  Is there a way to salvage files after a cold start?  Well,
within certain limits, there IS a way.

First, let's look at what happens after a cold start.  The cold-start
procedures are carried out in high RAM (above address 62335) where the
file directory resides.  Among other things, some housekeeping chores
are done, such as checking how much memory is available and initializing
the file directory that is displayed in Menu mode.  As near as I can
determine, the contents of low RAM from 32767 to 62335--where our precious
files are stored--are not disturbed.  That is, the directory is gone,
but the files are still there.  The trick is to find them.

Examining the contents of RAM is relatively easy, using the PEEK
command.  However, deciphering what is found in RAM may not be so easy.
Text files are stored in ASCII format and are readily recognizable.
BASIC files are stored in some sort of shorthand notation and, unless
there are some tell-tale REM statements at the beginning and ending of
each program, it takes a cryptologist to figure out where one BASIC
program stops and another starts and to decode the results.  Even if an
individual program can be recognized, it may very likely require more of
an effort to decipher it than to rewrite it from scratch.  For example,
a typical BASIC program line and the corresponding shorthand code is
shown below:

	20 E=(A+B+C+D)*10/4

	^TE (A B C D) ^O^J ^U


Notice that ^T happens to be ASCII Code 20 and ^J is Code 10, but ^U is
21.  What happened to 4?  And, where are the arithmetic operators?  With
enough time and effort, a conversion code could no doubt be developed,
but is it worth it?  So, for the time being, forget about recovering
BASIC programs and concentrate on TEXT files.  Of course, if the BASIC
program had been saved in ASCII format (using SAVE"file",A) it would be 
as easy to recover as a TEXT file.   However, it would require a little
more memory than a binary file and a few more seconds to load.

Basically, the technique for recovering lost files is as follows:

	1. Open a file that will be used to temporarily hold
	   the recovered portions of RAM.

	2. Read the contents of RAM, one byte at a time,
	   using the PEEK command.

	3. Write each recovered byte to the temporary RAM file
	   or, to be very safe, write to a cassette tape first
	   and then reload the file from tape to massage it.

	4. Edit out any unusable portions of the temporary
	   file to free up some space in RAM.

	5. Use the cut-and-paste feature to salvage the text of
	   interest and recreate the original text files.

	6. Delete the temporary file when finished.


Several articles have been published on the subject and it has been
discussed on CompuServe.  The articles that I can remember are:

	Richard Perry, Portable 100, November 1984
	Frank Oechsli, Bay Area NEC/100 Newsletter #6, June 1985
	  (Also, see correction in Newsletter #8, October 1985)
	Terry Kepner, Pico, February 1986


Although the various approaches used are very similar,  each have their 
strong points and weaknesses.  Oechsli suggested using a CLEAR statement
(CLEAR100,34767) to protect all but the first 2000 bytes of RAM.  Then,
a several-line BASIC program can be entered to examine the contents of
RAM and copy the useful sections to tape for protection and later
recovery.  However, the problem with using a line-numbered BASIC program
is that it is loaded into low RAM,  starting at 32767.  If anything of
recoverable value occupies that area, it will be overwritten and lost.

Kepner's approach was to use a compound, direct BASIC command
(unnumbered), which is executed from high RAM, leaving low RAM intact.

Now for the specifics of how to do it.   The following direct command,
entered as one continuous line, will do the job nicely:

	OPEN "Temp" FOR OUTPUT AS 1: PRINT"Standby...":
        FOR I=32767 TO 62335: PRINT#1,CHR$(PEEK(I));: NEXT I:
        PRINT"Done...": END


If a cassette file is desired, use "CAS:Temp" instead of "Temp".  The
"Temp" file will contain everything that was recovered from RAM and can
be examined in TEXT mode.  A CLEAR statement could be used to protect
most of RAM if the file is copied to tape or to the LCD (for scanning).
Obviously, the CLEAR statement cannot be used to protect RAM if the
recovery file will be created in RAM.   It is probably not necessary
anyhow, since the recovery file is being built in the area that has just
been read.  Of course, it is possible to make a typo while entering the
above program that would overwrite a portion of RAM that had not yet
been read.

If there were any BASIC programs in RAM before the crash, the first part
of the recovered file will contain what looks like a random assortment 
of alphabetic, numeric, and special characters.  Keep looking until a
recognizable text file is found.  Don't be alarmed if bits and pieces of
the original text file appear to be scattered throughout the recovery
file.  As files are moved around by Save and Kill commands, remnants of
earlier versions of the text files may be left at previous storage
locations and some of these remnants may have been overwritten, leaving
a hodge-podge of text scattered  throughout RAM.  Keep looking, a
complete, intact copy of each text file should be found somewhere in the
recovery file (except for portions which may have been damaged during
the crash).

Since the above program is generally needed only after a cold start, it
does no good to keep it stored in RAM.  Copy the program onto a 3x5 card
and keep it in the 8201A carrying case for THAT DAY.

BILL GRENKE
74756,235