Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!maryland!oddjob!uwvax!husc6!yale!bunker!wtm From: wtm@bunker.UUCP (Bill McGarry) Newsgroups: comp.dcom.modems Subject: Re: Information on TDD's (1 of 3) Message-ID: <1999@bunker.UUCP> Date: Thu, 30-Apr-87 21:57:16 EDT Article-I.D.: bunker.1999 Posted: Thu Apr 30 21:57:16 1987 Date-Received: Sat, 2-May-87 14:43:16 EDT References: <4262@fritz.UUCP> <1987@bunker.UUCP> <1997@bunker.UUCP> Reply-To: wtm@bunker.UUCP (Bill McGarry) Distribution: na Organization: Bunker Ramo, an Olivetti Company, Shelton, CT Lines: 179 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