Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!princeton!rocksvax!rocksanne!rph From: rph@rocksanne.UUCP (Bob Herloski) Newsgroups: comp.dcom.modems Subject: Re: modem interface to TDD (deaf communications), how? Message-ID: <248@rocksanne.UUCP> Date: Fri, 9-Jan-87 08:20:29 EST Article-I.D.: rocksann.248 Posted: Fri Jan 9 08:20:29 1987 Date-Received: Sat, 10-Jan-87 02:02:49 EST References: <763@sdcc12.ucsd.EDU> Reply-To: rph@rocksanne.UUCP (Bob Herloski) Distribution: na Organization: Xerox Corp., Webster, NY Lines: 34 Keywords: TDD deaf In article <763@sdcc12.ucsd.EDU> wa371@sdcc12.ucsd.EDU (Bernd) writes: >Is it possible somehow to use the typical 300 or 1200 baud modem to >link up with a TDD (telecommunications device for the deaf)?? >TDD is a slow speed teletypewriter or sorts. I just met a friend >who is deaf, and we have to communicate through a relay service, >where a third party (free of charge) reads for one and types for the >other while on the telephone. It is kind of backward, to put it >mildly. >I tried it at various baud settings of my terminal through a PASSWORD >modem. But although my modem said "connect", I got only garbage. This is how I understand the TDD protocol: (1) It is a 5-bit Baudot coding (2) Most (older) TDD's use FSK at 45.45 (or is it 55?) baud. (3) Since it is a half-duplex protocol, there is no difference between sending/ receiving/originating/answering frequencies: I believe that the mark and space frequencies are 1400 Hz and 1800 Hz (or it might be 1800 and 1400). This is unlike the standard Bell 103 protocol in your 300 baud modem. Several years ago I built a modem to act as a TDD interface for my C64; I'm sorry if I don't have the details exactly correct; my notes are at home. There are some newer TDD's that implement both the old style Baudot coding AND ASCII at 300 baud (switch-selectable). I hope this helps. (Comments and/or corrections from the net are welcome!) -- Bob Herloski ...!seismo!rochester!rocksanne!rph <<< No fancy signature >>>