Transmission system employing high impedance detection for carrier detection

A transmission system comprising:

• a transmitter comprising a tri-state driver having a data input terminal, an enable terminal and two output terminals, said data input terminal being supplied with a send data signal, said enable terminal being supplied with a request to send signal, said tri-state driver having a high output impedance state when said request to send signal has a first logic value and said two output terminals outputting complementary data signals in accordance with said send data signal when said request to send signal has a second logic value;
• a pair of transmission lines each having one end coupled to a corresponding one of the two output terminals of said tri-state driver;
• and
• a receiver comprising a data detector for detecting the complementary data signals from the pair of transmission lines to produce a received data signal when the tri-state driver is not in said high output impedance state, and a high impedance state detector for producing a carrier detect signal having a predetermined logic value to indicate that no carrier is present on the pair of transmission lines when a high output impedance state of said tri-state driver is detected.