Telecommunications Device for the Deaf
Telecommunications Device for the Deaf
(communications)The acronym TDD is sometimes expanded as "TelecommunicationDisplay Device" but is generally considered to be derived from"Telecommunications Device for the Deaf". The deaf themselvesdo not usually use the term "TDD", but prefer simply "TTY"-- possibly the original term. The ambiguity between this andthe other meanings of "TTY" is generally not problematic.The acronym "TTD" is also common The standard most used by TDDs is reportedly a survivor ofBaudot code. It uses asynchronous transmission of 1400 Hzand 1600 Hz tones at 45.5 or 50 baud, with one start bit,5 data bits and 1.5 stop bits. This is generallyincompatible with standard modems.
A typical TDD is a device about the size of a small laptop computer (resembling, in fact, a circa 1983 Radio ShackModel 100 computer) with a QWERTY keyboard, and smallscreen (often one line high, often made of an array ofLEDs). There is often a small printer for makingtranscripts of terminal sessions. An acoustic couplerconnects it to the telephone handset.
With the falling cost of personal computers and thewidespread use of Internet talk systems, there is nowlittle reason to use this Stone Age technology.