Newsgroups: bit.listserv.deaf-l
Date:         Wed, 18 Nov 1992 11:15:22 EST
Reply-To:     "Communication Disorder Discussion List" <CDMAJOR@KENTVM.BITNET>
Comments:     Resent-From: Jennifer Barber <JLBARBER@MIAMIU>
Comments:     Originally-From: Anthony Caruso <ACARUSO@KENTVM.BITNET>
Comments:     Warning -- original Sender: tag was CDMAJOR@KENTVM
From:         Jennifer Barber <JLBARBER@MIAMIU.BITNET>

I thought this may be of some interest to deaf-l. It was originally sent to
CDMajor by Dr. Anthony Caruso from Kent State University.
I will warn you that it is a long posting-457 lines.

Jennifer Barber
jlbarber@miamiu.bitnet
jlbarber@miamiu.acs.muohio.edu
----------------------------Original message----------------------------

---------------------------------------------------------------------

  This article is from the Handicappped Educational Exchange
  (HEX) bulletin board, accessible to both TDD's and Ascii
  modems.  HEX has two phone lines now: 1-301-593-7033 which
  is a 300 baud line which can handle either TDD or Ascii.
  The second line, 1-301-593-7357, is a 1200 baud Ascii only
  line.  My thanks to Dick Barth, the sysop of the HEX BBS
  for this article.  Dick's Internet address is:
  rbarth%ka3ovk.uucp@uunet.uu.net



          COMMUNICATING BETWEEN A TDD AND A COMPUTER

   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 or Baudot 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)
              ------------
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
and TDDs 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


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Subject: TDD info (2 of 3)
To: HORWITZ%KENTVM.BITNET@vm1.nodak.edu (PETER HORWITZ)
Date: Sun, 16 Feb 92 0:30:59 EST
 11:24 am
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  This article is from the Handicappped Educational Exchange
  (HEX) bulletin board, accessible to both TDD's and Ascii
  modems.  HEX has two phone lines now: 1-301-593-7033 which
  is a 300 baud line which can handle either TDD or Ascii.
  The second line, 1-301-593-7357, is a 1200 baud Ascii only
  line.  My thanks to Dick Barth, the sysop of the HEX BBS
  for this article.  Dick's Internet address is:
  rbarth%ka3ovk.uucp@uunet.uu.net


   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





======================================================================== 99
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From: wtm@sheldev.shel.isc-br.com (Bill McGarry)
Message-Id: <9202160530.AA03783@sheldev.shel.isc-br.com>
Subject: TDD info (1 of 3)
To: HORWITZ%KENTVM.BITNET@vm1.nodak.edu (PETER HORWITZ)
Date: Sun, 16 Feb 92 0:30:18 EST
 11:24 am
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Here are the usual articles that I send out for people
wanting to know more about TDD's in general and with PC's.


  This article is from the Handicappped Educational Exchange
  (HEX) bulletin board, accessible to both TDD's and Ascii
  modems.  HEX has two phone lines now: 1-301-593-7033 which
  is a 300 baud line which can handle either TDD or Ascii.
  The second line, 1-301-593-7357, is a 1200 baud Ascii only
  line.  My thanks to Dick Barth, the sysop of the HEX BBS
  for this article.  Dick's Internet address is:
  rbarth%ka3ovk.uucp@uunet.uu.net

            TELECOMMUNICATIONS DEVICES FOR THE DEAF

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.

======================================================================== 53
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From: wtm@sheldev.shel.isc-br.com (Bill McGarry)
Message-Id: <9202160529.AA03774@sheldev.shel.isc-br.com>
Subject: Re: PC to TTD communication
To: HORWITZ%KENTVM.BITNET@vm1.nodak.edu (PETER HORWITZ)
Date: Sun, 16 Feb 92 0:29:30 EST
 11:24 am
Return-Receipt-To: wtm@bunker.shel.isc-br.com
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Hi Peter,

This question comes up so frequently that I am going to
try to answer it myself.  A TDD "talks" Baudot code while
your modem on the PC talks Ascii.  This means that the two
cannot communicate with each other unless:

1. The TDD has the capability to switch into Ascii mode
which some TDD's have.  Then the PC and the TDD can communicate
and I have some demos of software that can help there.

2. You have a IBM PC with the cassette tape player jack in
which case there is software called TDD54 and TDD56 which
will work.

3. You build a hardware TDD interface for your PC.

Unfortunately it cannot be done through software.

I have a set of three files which describe this in more
detail which I will send to you.


If you have any more questions, let me know.

                                Bill McGarry
                                (203) 337-1518

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