A Programming Caution re the Alternate LCD Buffer
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There is a lot (well, some!) interest in using the alternate LCD buffer to
run small M/L programs in.  SORTHI.CO (from SORTHI.100) and TEXT.CO (from
NOWRAP.100) are two such Model 100/102 programs.  The thinking is that
there are 320 available bytes up there, starting at FCC0h (64704d).  Well,
not quite!

If you use the routine at 5AABh to search for a file on the directory, be
careful!  It uses an area in the alt LCD buffer for temporary storage
(starting at FDD9h) -- and can overwrite part of you code.
 
I just discovered this -- and that's the primary reason my earlier
attempts to expand my program SORTHI to do other things (e.g., FILES on
screen) had failed.  If you use the 5AAB routine at the start of the
program, you can then use the area it writes to as data buffers (i.e., put
them right at the end of the source).

I discovered this when my last message came up with the name of the file I
was processing replacing the end of it.  Quite a puzzling hour.  Earlier,
it was overwriting my code, with no symptoms other than a trip to
never-never land.
 
It appears that any program not using this function can be 320 byte in
length (will show as 326 bytes on the menu).  If you use this function,
282 bytes (288 bytes on menu) are OK -- and above that the space can be
used for buffers AFTER the use of the function at 5AABh (find a file in
the directory).


Phil Wheeler -- 71266,125
2 August 1987