How the Linefeed Utilities Work
-------------------------------

This is how the print linefeed patch in FIXLF/LFUTL (and LFEED.200
) works.  The string poked into the F8 key memory location in high
RAM installs a machine language program into the definition for 
this key:

  dec   hex      code
  ---   ---   -----------
  254    FE
   13    0D   CPI  0Ah   ;is it a CR?

  245    F5   PUSH AF    ;save accum on stack

   62    3E
   10    0A   MOV  A,0Ah ;put LF in accum

  204    CC
   63    3F
  109    6D   CZ   6D3Fh ;ROM call to print LF if CR was found

  241    F1   POP  AF    ;restore the accum char at entry

  201    C9   RET        ;return to normal print routine


This program is entered from the print routine in high RAM, if the
patch defined by A (in FIXLF/LFUTL) is poked in to cause the jump;
the pokes make the print routine jump to the F8 area where this 
program resides.

All M100 print LF patches appear to work in this manner.  It's all
a matter of where the code is installed.  In a print processor 
such as LAPWRD it can be installed within the program.  In 
LPTLF.100 it is placed just under MAXRAM, a disaster if other m/l 
programs want that space.  It is also possible (recent DL4 file) 
to put it into the bottom of RAM (first Basic program); but there 
it can conflict with SUPERA and/or the PG Designs MENU utility.

The function key location is surprisingly safe.  However, it will 
be zapped by any Basic program which has the following code (M100 
manual, p.149):

  CALL 23164,0,23366
  CALL 27795

or M/L programs with equivalent code.  A common offender is the 
original WRITE+.BA from PCSG (aka SCRIPTSIT, more or less) -- 
which reset the keys (without ever having changed them, so this 
superfluous code can be removed).  Hugo Ferreya wrote FIXLF.HF1 (I
think in response to a message of mine) and uploaded it here.  
I've used it for about two years with no problems.

Phil Wheeler -- 71266,125