PCHXMD.CO

                     ENHANCED VERSION OF XMD100.CO.
                     Wilson Van Alst [76576,2735]

                                8/23/87


Credit to J R Chenoweth for the original machine language XMODEM program,
XMD100.CO -- the only one allowing error-checked transfers that take
advantage of superspeed modems.

XMODEM programs written in BASIC may be fine at 300 bps, but they can't
keep up at 2400 baud.  Compare:


                  6985 byte XMODEM download
                   CIS connect at 2400 baud

                  XMDM26.BA      3:04
                  XMD100.CO       :58


But XMD100 has a couple of drawbacks: a reputation for being "buggy," and
a failure to allow high-speed normal (non-XMODEM or "capture") transfers.
They are limited to about 600 baud because the M100 interrupts data flow
while it sloooowly scrolls its screen.

PCHXMD fixes the latter problem by setting F6 as a toggle, to turn scrolling
on and off, in the TERM mode.

I'm not familiar with all the bug reports, but personal experience has shown
the program to work well -- once you manage to install it.  I had persistent
difficulties using LOAD.BA to convert XMD100.HEX.  I downloaded the hex file
twice; and despite proper checksums, it would not produce a bug-free version
of the .CO program.  I finally went to XMD26, downloaded the hex file with
XMODEM protocol, and got it to work.

To help avoid those problems, PCHXMD.HEX is designed for conversion with
CHANGE.BA -- which includes internal checksumming of the code it installs.

Note that you must run PCHXMD.CO with a basic "driver" program -- listed
as PCHXMD.DRV in the same DL.  With comments removed, it is about 50 bytes.
If you re-locate the main program, you'll have to change the poke values in
the driver (see "Nasty stuff," below).


Step-by-step instructios to run:

  1.  Download PCHXMD.HEX, PCHXMD.DRV, and XMD100.DOC files.  You'll also
      need CHANGE.BA and its documentation, if you don't already have them.

  2.  Use CHANGE.BA to convert PCHXMD.HEX to PCHXMD.CO (the file name
      expected by the driver program).

  3.  Strip PCHXMD.DRV to the bare essentials and install it as PCHXMD.BA,
      or whatever you choose to call it.

  4.  Use the .BA file to run the .CO program, per instructions from
      XMD100.DOC -- with the new feature of an F6 key that toggles screen
      scrolling off and on.


NASTY STUFF

This program looks like it uses RAM from 59381 to 62285.  In fact, it uses
memory all the way to MAXRAM for variables and buffering.  I don't know if
this "extra" space is absolute (keeps the same location, wherever you put
the main program) or relative (changes address if you relocate the main file).
So be prepared for the worst if you try installing this BELOW other m/l
programs.


NICE STUFF

Most of all, you'll save money.  I used to spend about 30 minutes a day on
CIS, reading messages at 300 baud, then selectively re-reading them for
download if I wanted the contents.  Now I do a 2400 baud no-scroll download
of an entire day's messages in less than 3 minutes.  I used to "capture"
stuff and hope for no transmission glitches.  Now, I let XMODEM do the
driving and know I'm getting what's really there.

In addition, with an external modem, this program will let you go back into
the M100's main menu and use BASIC and TEXT without breaking the connection
to a host.  Simply run the driver program again (or CALL HIMEM+20 from BASIC)
and hit the TERM key to get back on-line.  I've even pulled the modem's
RS232 cable out of the M100, attached the TDD cable, moved a file to disc
(using TS-DOS on ROM), and swapped cables again without a disconnect.

What's missing:  Auto-dial and auto-logon.  I hope to add those, when time
permits, either as a supplement to the driver program or as a "patch to the
patch" in assembly.