Telecommunication device operating under an enhanced TDD protocol

An enhanced telecommunication device for the deaf (TDD) for communication over a telephone line, the device comprising

• a source for input data characters to be transmitted;
• a destination for received data characters;
• a microprocessor operating in accordance with a stored program code and connected to accept input data from the input source and to deliver data characters to the destination;
• an analog input line adapted to being connected to the telephone line so as to be responsive to the reception of Baudot tones over the telephone line and also connected to the microprocessor so as to provide a digital input to the microprocessor of the data received over the telephone line;
• an analog output circuit adapted to being connected to the telephone line so as to be capable of presenting Baudot tones over the telephone line and also connected to receive data from the microprocessor and transmit Baudot tones encoding such data over the telephone line;
• and
• a memory device connected to the microprocessor containing the program code for operation of the microprocessor to control operation of the telecommunications device to generally
• (i) receive data entered from the input source,
• (ii) present data entered from the input source on the analog output line,
• (iii) receive data from the analog input line and
• (iv) deliver data from the analog input line to the destination;
• the program code further comprising code
• (a) enabling communications under either a conventional Baudot protocol or an enhanced TDD protocol which transmits data using Baudot tones without transmitting a carrier when no data is being sent, the data being transmitted at a data transmission rate which exceeds an average rate of 100 baud and which includes mark bits and space bits of different bit time intervals,
• (b) causing a special synchronization sequence to be transmitted under the enhanced TDD protocol, which sequence is made up of 1400 hertz tones and echo suppression tones, the sequence selected to be a sequence which is not recognized as a displayed character by a remote telecommunications device operating under conventional Baudot protocol, and
• (c) causing the timing and format of communications to be in conventional Baudot protocol if no synchronization sequence is received in return from the remote telecommunications device and in enhanced TDD protocol if a synchronization sequence is received in return from the remote telecommunications device.

A telecommunication device for the deaf (TDD) comprising

• a keyboard;
• a visually readable display;
• a microprocessor operating in accordance with a stored program code and connected to accept input data characters from the keyboard and to present data characters on the display;
• an analog input circuit adapted to being connected to a telephone line so as to be responsive to the reception of Baudot tones over the telephone line and also connected to the microprocessor so as to provide a digital input to the microprocessor of the data received over the telephone line;
• an analog output line adapted to being connected to the telephone line so as to be capable of presenting Baudot tones over the telephone line and also connected to receive data from the microprocessor and transmit Baudot tones encoding such data over the telephone line;
• and
• a memory device connected to the microprocessor containing the program code for operation of the microprocessor to control operation of the telecommunications device to generally
• (i) receive data entered from the keyboard,
• (ii) present entered data from the keyboard on the analog output line,
• (iii) receive input data from the input analog line and
• (iv) display data from both the keyboard and the input analog line on the display;
• the program code further comprising code enabling communication under either a conventional Baudot protocol or an enhanced TDD protocol, the enhanced TDD protocol using a seven-bit character set, using the Baudot tones of 1400 Hertz for a logical one and 1800 Hertz for a logical zero, and having a bit time for a space of 12 milliseconds and a bit time for a mark of 7 milliseconds.

A method of using a telecommunication device for sending characters received from a user over a telephone line to a recipient telecommunications device comprising the steps of

• accepting a series of input characters from the user,
• storing the series of characters in the form of digital data in memory in the telecommunications device,
• transmitting the series of characters over a telephone line as a sequence of tones encoded in an enhanced TDD protocol in which (i) Baudot tones of 1400 and 1800 hertz are used to represent data bits when data is being sent with no tones being transmitted when no characters are being sent, (ii) the bit times for a logical space bit and for a logical mark bit are different in time so as to minimize the total time required for character transmission, (iii) each character is represented by seven bits, (iv) the characters are encoded using an ASCII character set, and (v) the average rate of character transmission is in excess of 100 baud, and
• receiving sequence of tones at the recipient telecommunications device and decoding the series of characters therefrom.

A telecommunication device comprising

• a keyboard for accepting a series of input characters from a user,
• a display for displaying the characters which are input by the user,
• a microprocessor connected to the keyboard and the display for receiving and displaying the series of characters,
• a memory connected to the microprocessor for storing the series of characters and for storing program code for operation of microprocessor to control operation of the telecommunications device,
• an analog output circuit connected to the microprocessor and adapted for linkage to a telephone line, the analog output circuit capable of generating Baudot tones of 1400 and 1800 hertz, and
• the program code causing the microprocessor to direct the analog output circuit to transmit the series of characters onto the telephone line in an enhanced TDD protocol in which (i) Baudot tones of 1400 and 1800 hertz are used to represent data bits with no tones being transmitted when no characters are being sent, (ii) the bit times for a logical space bit and for a logical mark bit are different in time so as to minimize the total time required for character transmission, (iii) each character is represented by seven bits, (iv) the characters are encoded using an ASCII character set, and (v) the average rate of character transmission is in excess of 100 baud.