Communications Between TTYs and Computers

Can a computer with a regular modem communicate with a TTY?

No, a regular computer modem cannot communicate with a TTY.  However, there are specialized TTY-compatible that can be used with your computer’s communication software to “talk” with TTYs.

What is the difference between how a modem works vs. how a TTY works?

TTYs and computers communicate in different “languages” and at different speeds.

In the U.S., most TTYs use a language or “communication code” called Baudot to transmit signals over the phone lines at a speed of 45.5 baud. When a person types on his or her TTY, the letters are translated into sounds that are sent through the phone lines to the TTY at the other end of the line. The receiving TTY converts the Baudot signals back into letters and displays them on the screen.

All computers with standard modems transmit signals at a speed of 300 baud in a language called ASCII code. Computers do not understand Baudot. Since Baudot and ASCII are not compatible, TTY users and computer users can not talk to each other without specially adapted equipment.

Can I get special equipment for my computer so I can call TTYs?

There are specialized computer modems that understand Baudot (TTY) code. Some of these modems come with software that lets the computer perform like a TTY and communicate with text telephones.

How do I use the ASCII option to call a computer with my TTY?

Your TTY must include with ASCII code, which allows the TTY to communicate with a computer that has a standard modem (the modem must support a 300 baud transmission rate).  Before placing a call, the TTY user must turn on the ASCII code option.

Ultratec TTYs that include ASCII (optional):

  • Superprint Pro80
  • Superprint 4425
  • Supercom 4400

I have a Superprint 4425, how do I call a computer?

First, make sure your Superprint 4425 has ASCII code; look on the bottom of the TTY to see if the ASCII square is marked.

Receiving a call:

Upon answering calls, your Superprint 4425A will automatically try to connect in ASCII code first and then default to Baudot (TTY) code.

Placing a call:

If you wish to make an outgoing ASCII call, you will need to turn the ASCII code on before making your call. To do this:

  • Hold down the key and press the 0 key
  • Press the space bar until you see CODE (ASCII)
  • Press the key
  • The display will say ASCII CODE ON
  • Now dial the number you are calling

Your settings must match the settings of the person you are calling. You may want to notify the person you are calling that your ASCII communication settings are: 300 baud, 8 bit, No Parity, 1 stop bit, half duplex.

More ASCII Information


ASCII stands for American Standard Code for Information Interchange. Some TTYs and all computers in the United States and Canada use ASCII. If your TTY has ASCII, you may need to change some options. To connect a Superprint Pro80 to a computer, the other person should have the computer set to use 300 baud, half duplex, 8N1 parity and CR.

Definitions of ASCII Options


Determines which machine is calling and which one is answering. This usually happens automatically. However, if you are manually setting up ASCII, select ORIGINATE if you are going to be the person placing the call and select ANSWER if you are going to be receiving ASCII calls.

Baud Rate (110/300)

Determines how fast the signals travel through the phone lines. You can choose 110 or 300 baud, but 110 is rarely used.

Duplex (HALF/FULL)

Controls how characters are displayed. If you get double characters (lliikkee tthhiiss) or none at all, change the option between half duplex and full duplex.

Parity (8N1/7E1)

Controls error-checking. You can choose 8N1 or 7E1. The first number is data bits. The middle letter means: “N” for No parity or “E” for Even parity. The last number is stop bits.

Return Sequence (CR/CR + LF)

Determines what the TTY sends when you press the key. You can choose CR or CR + LF. CR stands for “carriage return” and CR + LF stands for “carriage return plus line feed.” A carriage return goes to the beginning of the current line. A carriage return plus a line feed goes to the beginning of the next line.

ASCII Seek Time (3)

Sets the length of time during which the TTY sends out an ASCII seek tone. The normal TTY seek time is 3 seconds. You may need more time if you often connect to computers. Six seconds is recommended. Selecting 0 turns off ASCII code and your TTY will not try to use it even if the other TTY is using ASCII.

Troubleshooting ASCII Calls

If you do not receive a clear message during an ASCII call, try:

  • Changing the parity setting to correct garbled strings of text.
  • Changing the duplex setting to correct no characters or double characters appearing when you type.
  • Changing the baud rate (110 or 300).
  • Changing the ASCII (ORIGINATE/ANSWER) setting.

If the code option is set to automatic and your TTY loses the ASCII connection, NO ASCII CONNECTION is displayed and Baudot is used.

If the code option is set to ASCII and your TTY loses the ASCII connection, it waits until the other person changes to ASCII or until you change the code option setting to automatic or Baudot.

If you are unable to make an ASCII connection, check to make sure your ASCII seek time is set to at least 3. You can also try increasing the seek time.

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