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TDD5PT2.DOC
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1985-03-20
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TDD5PT2.DOC
Deaf people in this country have, over the past quarter century
or thereabouts, adopted the "TTY" or "TDD" as their standard means
of communicating over the telphone. "TTY" is of course a contraction
for "Teletype", a trademark of the Teletype Corporation. "TDD"
stands for "Telecommunications Device for the Deaf".
The original TDD was a teletype machine, and the modem used
was one designed for the specific purpose of deaf communications by
Dr. Robert Weitbrecht. It is not compatible with any standard Bell
modem design, as the TDD is incompatible with modern computers.
Computers of course use ASCII while the TDD uses the Baudot code
transmitted at 45.5 baud. A description of the TDD and the
Weitbrecht modem are given in the file "TDD.TXT".
The old mechanical Baudot teletype machines still serve many
people as their working TDD. However, many newer devices of more
modern design have come on the market, some incorporating a modem
with a keyboard and an LED or LCD display. In addition, modern
computers often serve the place of a TDD, since they are perfectly
capable of converting between the ASCII and Baudot codes. Some
computers, in fact, are able to replace the modem as well. The
IBM-PC is one of these.
In order to make the PC serve as a TDD, it is only necessary to
install appropriate software (available for downloading in the files
TDD5PT2.EXE and TDD5PT2.ASM) and connect the computer to the
telephone line in some suitable fashion. One suitable approach is to
use the technique designed by the author of the software; it employs
a Radio Shack telephone amplifier, a couple of plugs, jacks and
switches, and a little soldering. As an alternative, the complete
device can be purchased for $40 from a group in Texas who are
working in the field of rehabilitation.
The software was written, and placed in the public domain, by
John Spalding of Atlanta Georgia. He has made it available for
distribution to the Handicapped Educational Exchange (HEX) which I
operate. Further information on the telephone interface can be
obtained from the address below. If you want a copy of the software
on disk, send me a formatted disk and a self-addressed mailer with
postage attached, along with a note as to what you want.
Similar software by John Spalding is available for the Tandy
Color Computer. This machine also serves as its own modem, and
employs the same telephone coupling device. Software by other
authors (most local and members of AMRAD, the Amateur Radio Research
and Development Corporation) is available for the TRS-80 model I,
PET, Atari, Apple, VIC-20, Commodore 64 and Smoke Signal
Broadcasting 6800 and 6809 machines. These other programs require an
external modem (plans for which are available) and are also in the
public domain; design data are available for the cost of
reproduction and mailing.
For further information contact:
Handicapped Educational Exchange
11523 Charlton Drive
Silver Spring MD 20902
The HEX BBS operates 24 hours a day on (301) 593-7033, using
300 baud only and settings of 8-N-1. It can also be accessed using a
TDD. I can be contacted by voice on (301) 681-7372 evenings (at a
reasonable hour, please) and weekends. The AMRAD and HEX crew look
forward to your comments regarding the above software, and to your
questions and information on all aspects of the use of computers to
assist the disabled.
Richard Barth