wtm@bunker.UUCP (Bill McGarry) (05/01/87)
These three articles are taken from the Handicapped Educational
Exchange (HEX) bulletin board (301-593-7033, 300 Baud). These articles
will be posted on a periodic basis in the misc.handicap news group.
Other information, comments, questions, etc, on TDD's are posted in
the misc.handicap news group and the Handicap Digest mailing list.
Thanks to Dick Barth, the sysop of the HEX BBS for these articles.
Bill McGarry
Moderator Handicap Digest/News
Bunker Ramo, Shelton, CT
(203) 337-1518
PATH: {philabs, decvax, fortune, yale}!bunker!wtm
TELECOMMUNICATIONS DEVICES FOR THE DEAF
(Posted April 30, 1987)
There are over 3000 Telecommunication Devices for the Deaf
in use in the greater Washington D.C. area and estimates range
as high as 25,000 nationally. The deaf have been using these
devices for over fifteen years, to communicate among themselves
and more recently, with a growing number of organizations with
TTY numbers to allow phone access to deaf users. See the INFO
files for some numbers. Although originally the majority of
devices were surplus "teletype" machines donated by the phone
company and the military, these mechanical printers are rapidly
being replaced by more modern devices offering special features
as well as reductions in size and weight. A portable device
about the size of a calculator is available for under $200.
The following shows the differences between the modems used.
The owner of a computer can rather easily modify his software to
convert between the ASCII code used in microcomputers and the
code used by the deaf TTY. Often, it is harder to get a modem
which is compatible both with a computer and with the TTY. The
usual procedure is to convert an ASCII (Bell-103 compatible)
modem or build a TTY modem from scratch.
There are several differences between protocols used by
ASCII terminals and by the TTY. The following attempts to
clarify these.
ASCII DATA DEAF TDD
FEATURE COMMUNICATIONS COMMUNICATIONS
------- ------------------ --------------
CODE ASCII Baudot
SPEED 110/300 baud 45.45 baud
MODE full/half-duplex 2 way simplex
MODEM Bell 103 ORIG/ANS Weitbrecht
MARK ORIG 1270 Hz 1400 Hz
ANS 2225 Hz
SPACE ORIG 1070 Hz 1800 Hz
ANS 2025 Hz
In the Weitbrecht modem, tones are only transmitted for the
duration of the character so the line is available for
transmission in either direction. In practice the mark tone is
retained for as much as a half second before being squelched.
Notice also that the mark is high for the Bell 103 and is
the low tone for the Weitbrecht. This means that in converting a
a Bell 103 modem to TTY use, the data will be inverted from
RS-232 and the mark hold circuitry will need to be inverted.
Line supervision is also different in these modems. In -103
protocol, the presence of the tone carriers gives positive
indication of the status of each end of the link. In the
Weitbrecht case, however, the absence of tones except while
characters are being transmitted results in there being no
positive way to test the status of the other end of the
communications link. To aid the deaf, a lamp is provided on most
Weitbrecht modems which varies in intensity proportional to
signals on the line so that the ringing and busy signals are
recognizable.
Federal Government numbers
____________________________________________________________
Deafness and Communications Dis. 202 245-0591
Department of the Treasury 202 287-4097
Internal Revenue Service (toll free) 800 428-4732
Merit Systems Protection Board 202 653-8896
Nat'l Air & Space Museum (24 hours) 202 357-2853
National Ocean Atmospheric Administration 301 427-7627
President's Comm on Employment of H'capped 202 653-5337
Smithsonian Institution 202 381-4233
Social Security 800-325-0778 MO] elsewhere 800 392-0812
U.S. Government Printing Office 202 541-2977
U.S. Department of Commerce 202 377-5588
U.S. Senate 202 224-5644
USOE Office of Special Education 202 472-1356
White House - GEN. INFO 202 456-6213...TOURS 202 456-2287
National TTY numbers (non-government)
____________________________________________________________
TTY Assistance Operator (toll free) 800 855-1155
American Express Co
American Express TOLL FREE (outside NY) 800-221-9950
TOLL FREE (inside NY) 800-522-1897
The above numbers are answered 9AM-5PM Eastern. The
following are for refunds of AMEX travelers checks, and
operate 24 hours a day.
TOLL FREE (outside NY) 800-221-9986
TOLL FREE (inside NY) 800-522-5538
American Airlines 800-582-1573 in Ohio- else 800 543-1586
United Airlines (toll free) 800 323-0170
TWA 800-252-0622 in Calif] elsewhere 800 421-8480
Greyhound Bus (toll free) 800 345-3109
AMTRAK (toll free) 800 523-6590
Deaf Crisis Center (toll free) 800 446-9876
Deaf Counseling Ctr (toll free) 800 446-5000
Western Union 800 392-1474 in MO] elsewhere 800 325-4108
Boston DEAFNET (DCI) 617-975-0354wtm@bunker.UUCP (Bill McGarry) (05/01/87)
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 22106-6148wtm@bunker.UUCP (Bill McGarry) (05/01/87)
These three files are taken from the Handicapped Educational Exchange
BBS (HEX). My thanks to Dick Barth, the sysop of HEX.
Bill McGarry
Bunker Ramo, Shelton, CT
(203) 337-1518
PATH: {philabs, decvax, fortune, yale}!bunker!wtm
On 23 January 1987 Michael Gallagher uploaded a file on TDD
communications. Slightly updated, here it is.
----------
COMMUNICATING BETWEEN A TDD AND A COMPUTER
(Posted April 30, 1987)
A TDD is a "Telecommunication Device for the Deaf." Also known
as a TTY, a TDD usually looks like a small portable typewriter
and runs on batteries and/or house current. If people on both
ends of a telephone call have one of these devices, it is
possible for them to communicate by typing out their messages
instead of speaking them. The message one person types on his
TDD appears on a little screen on the other person's TDD.
This is an exciting advance for hearing-impaired people
because it makes it possible for them to talk directly with
others who have these instruments and to do so by means of the
ordinary telephone.
Many people who buy TDDs quickly see the similarity between
these instruments and a personal computer. We often receive
inquiries from TDD users wanting to know if they can communicate
with someone who has a personal computer. The unfortunate fact
of the matter is that the two systems are basically incompatible.
One of the differences between a TDD and a computer is that
each uses a different coding system to transmit messages over
ordinary telephone lines. TDDs convert typewritten characters
into audible tones using the Baudot code system, while computers
use a coding system known as ASCII. The conversion of Baudot
code (from a TDD) into ASCII code (for a computer) can be done
easily through software, but the major problem is the speed of
signal transmission. TDDs use a baud rate of 45.5 bits per
second, while the designers of the integrated circuits used in
computers did not provide for speeds below 110 baud. Some
special hardware and software magic must be worked to meet the
lower speed standard for the TDDs.
(NOTE FROM HEX: This is not completely accurate. The
ICs in computers (specifically, the UARTS used to send
characters to a modem, a printer, etc.) can send data at just
about any baud rate. The problem is that some of them can't
provide the word structure used by Baudot. ASCII uses one start
bit, eight data bits plus either one or two stop bits; one of the
data bits may be used for parity. Baudot, on the other hand, uses
one start bit, five data bits, and 1.5 stop bits. (Strictly
speaking, there are 1.42 stop bits, but let's not quibble.) Some
UARTs are designed strictly for ASCII, and can provide 7 data
bits plus parity, or eight data bits and no parity, and either
one or two stop bits. Others (such as the 8250 used in the IBM-PC
and the 8251A used in the HEX BBS) can provide either ASCII
format or0Baudot format. END OF HEX NOTE)
.....
We have heard about several modems for computers that enable a
personal computer to communicate directly with a TDD by changing
the signals of each instrument into signals for the other, and
by changing the baud rate. We have not seen these instruments
demonstrated, so we mention them here without endorsing them.
------------
1. Phonetype 1000 C
Applied Communications
Belmont, CA
------------
2. Tele-Aide
Applied MicroSystems, Inc.
P.O. Box 832
Roswell, GA 30077
------------
3. SM85 SMART/modem
Krown Research, Inc.
6300 Arizona Circle
Los Angeles, CA 90045
------------
(NOTE FROM HEX: The forgoing are not modems in the strict
sense, in that a modem changes digital signals to tones and
vice versa. Units that provide code translation between ASCII
and Baudot in addition to modem functions have both advantages
and disadvantages compared to true modems. The advantages
include their ability to operate without a separate computer;
they can be used with a dumb terminal. Their disadvantages
include a lack of flexibility, since the user can't change the
program they're used with. The following produce true modems
which come with software fand the IBM-PC, or which can be used with
your own software if you prefer. Each produces both 110 and 300
baud ASCII, and standard TDD communications:
------------
Model CM-4 Smart Modem (ASCII and TDD, connects to computer
Phone-TTY Inc. serial port via RS-232 cable.)
202 Lexington Avenue
Hackensack NJ 07601 201-489-7889 (V/TTY)
0 ------------
Integrated Microcomputer Systems board modem plugs into
Rockville MD the IBM-PC bus
------------
END OF HEX NOTE)
The Tele-Aide system is for the Apple II Plus computer. In
addition to handling communication between a TDD and the Apple
computer, it contains an added feature that makes it possible
for a hearing-impaired person to communicate with a hearing
person who has a Touch Tone telephone. The hearing person
spells out his message for the hearing-impaired person by
tapping on the Touch Tone buttons. The message is spelled out
on the hearing-impaired person's computer screen. The
hearing-impaired person answers simply by talking.
The Novation Company's Apple-Cat II (tm) is a special modem
with software that enables an Apple to communicate with a TDD.
We don't know if it is available for other brands of computer.
We have heard from John W. Spalding (73165,203) that he has
developed systems for both the TRS-80 Color Computer and the
IBM PC jr. He has been kind enough to upload his programs to
DataLibrary 3 for those of you who are interested.
We have also heard from Robert Eveleigh (76475,1231) that he
is selling a TDD/Computer Interface for the Commodore 64 and the
Vic 20. His device is based on a design taken from
"The Transactor," Vol. 6, #2. He reports that he has added an
"au to-answer" featureto it so that no one has to be home to
take messages. He is selling this Interface and related
software for $60 (Deduction if you are hearing impaired).
You may contact him through the CompuServe number given above.
He is also interested in producing these devices for otler
types of computers. Let him know the brand and model.
Two companies that make TDDs with an ASCII switch on them are:
------------
Ultra Tec
6442 Normandy Lane
Madison, WI 53179
------------
and
------------
Krown Research, Inc.
6300 Arizona Circle
Los Angeles, CA 90045
------------
One group that has been trying to make it possible for computers
and TDDs to communicate is the Amateur Radio Research and
Development Corporation (AMRAD), a nonprofit group of volunteers.
AMRAD has established a computer system called HEX (Handicapped
Educational Exchange) which can accept calls from ASCII terminals
and0TDDs on the same phone line. In ASCII mode, it answers 300
baud. They have a lot of good information on line, including a
complete technical description of the Weitbrecht modem (the one
used by people with TDDs). AMRAD has plans available for modifying
Bell 103 type modems for TDD use. The phone for HEX is
301-593-7033. The phone for the AMRAD computer Bulletin Board
System is (703) 734-1387; this is a Fido system which is ASCII
only, 300 or 1200 baud, 24 hours a day. AMRAD's address is
P.O. Drawer 6148
McLean VA 22106-6148
As we said above, the newer TDDs coming on the market have
a switch on them that allows the user to go back and forth
from Baudot to ASCII.
David Manning
The Mainstream Center at
Clarke School
Northampton, MA
As modified by Richard Barth,
System Operator of the HEX