-=> Quoting Henri Derksen to Jasen Betts <=-

 HD> In the Netherlands (Europe) DTMF is also used for the TextTelephone
 HD> systems for the DEAF people to "talk" to each other.
 HD> Special DTMF-modems are used to convert DTMF tones to a DTMF charater
 HD> and after that to convert a string of characters to an ASCII character.

In the US the units use special modems, but the original units were
modified teletypes. That meant they used the 5-bit Baudot character
code. And the modems were originally hand buiult by ham radio
operators. They were half duplex. I think they used 1800 Hertz as
"mark" (1) and silence as "space" (0). And they ran at
the "standard"
45.45 baud.

So that was the standard. Later, Bell 103 was added to some units
giving them 300 baud ASCII capability. But the old Baudot code with the
weird modulation is (as far as I know) still standard. 

And the few standalone modems that'd do deafy TTY were *expensive. $300
in the mid 80s.  

I understand that the capability is buried somewhere in the Rockwell
chipsets of the last 5-10 years, but I've never seen any docs on that. 

I *have* seen plans for a simple circuit that you hook to the cassette
port on an IBM PC that with a simple driver turned the PC into a deaf
TTY unit.

--- FMailX 1.60