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From: wtm@bunker.UUCP (Bill McGarry)
Newsgroups: comp.dcom.modems
Subject: Information on TDD's (2 of 3)
Message-ID: <1998@bunker.UUCP>
Date: Thu, 30-Apr-87 21:54:38 EDT
Article-I.D.: bunker.1998
Posted: Thu Apr 30 21:54:38 1987
Date-Received: Sat, 2-May-87 14:42:36 EDT
References: <1987@bunker.UUCP> <1997@bunker.UUCP>
Reply-To: wtm@bunker.UUCP (Bill McGarry)
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Organization: Bunker Ramo, an Olivetti Company, Shelton, CT
Lines: 85

These three articles are taken from the Handicapped Educational 
Exchange (HEX) BBS (Thanks to Dick Barth, the sysop/creator of
HEX).

				Bill McGarry
				Bunker Ramo, Shelton, CT
				(203) 337-1518

     PATH:  {philabs, decvax, fortune, yale}!bunker!wtm


                        COMPUTER TDD's

(Posted April 30, 1987)

   It is possible to use a home computer as a TDD. This
requires programming to convert the ASCII code used by the
computer to the Baudot code used by the TDD, and vice versa. It
is usually necessary to add a special modem, unique to the TDD,
that is named after its developer, Robert Weitbrecht. A description
of this modem, and the characteristics of the TDD, are in INFO file T.
 
   John W. Spalding of Atlanta, Georgia has developed programs
for the Radio Shack Color Computer which permit it to serve as a
TDD without the need for a special modem. This design is a major
breakthrough since unavailability of these modems has been a
problem for those trying to make a computer talk to a TDD. Mr.
Spalding has placed his creations in the public domain, making
them available without charge to anyone who wants them. He has sent
HEX the source code; you may read it by selecting INFO files C1 for
the original version (TDD3.5) and C2 for the latest revision
TDD4.3 which is relocatable and able to placed in ROM. The two
are functionally equivalent and different only in relocatability.
An intermediate version (TDD4) which was available earlier has bugs
and is not recommended for use.

     All CoCo software is in assembly language for the 6809. They
are source only; machine code is not included. If you want a paper
copy including machine language, send a stamped self addressed
business envelope to:
  Handicapped Educational Exchange
  11523 Charlton Drive
  Silver Spring MD 20902

Machine code for TDD3.5 is available from HEX on cassette tape and
for TDD4.3 in a 2716 EPROM. The EPROM must be mounted in a ROM pack
to be inserted in the side of the CoCo. An empty ROM pack is available
for $9.95 from Spectrum Projects, P.O. BOX 21272, Woodhaven NY
11421 or call (718) 441-2807. Other sources for these ROM packs
may also be available. When you have received your ROM pack, 
contact HEX for information on getting an EPROM.

   Mr. Spalding has also written TDD software for the IBM-PC that,
like his CoCo software, does not require a modem. This is also in
the public domain and will be provided gratis to anyone who sends
HEX a blank, 5 1/2 inch floppy disk and return postage. A users'
manual covering design and use of both the PC and CoCo software comes
with the code.
 
   While neither the CoCo nor the IBM-PC TDDs requires a modem, it
is necessary to couple the computers to the phone line. Mr. Spalding's
way of doing this is with a Radio Shack telephone amplifier.
Design details on this are available from HEX, if you're willing to
modify the amplifier according to instructions. If you prefer
to get your equipment ready to plug in, the modified amplifier is
available from John Steele, 2100 North New Road, Waco TX 76707.
It plugs into, and can be used with, either the CoCo or IBM-PC 
using the Spalding software.

   Mark Becker has developed a program for the Altair 680b
using the 6800 microprocessor which is intended to be used for
radio teletype. It provides conversion between ASCII and Baudot,
and can be adapted to permit other 6800-series machines to work
as TDDs. It is also in the public domain, and is in INFO file C3.

   Conversions for the Apple, TRS-80 model I, Atari 400, Pet,
Smoke Signal Chieftain 6800 and 6809 machines were done by 
various members of AMRAD, the group which sponsors the HEX. 
Design information and software for these are in the public
domain and can be obtained for the price of reproduction and
mailing (roughly 12 cents a page) from AMRAD's Corresponding
Secretary, Howard F. Cunningham. He may be reached at:
   AMRAD
   P.O. Drawer 6148
   McLean VA 22106-6148