The Transmitter section accepts complementary TTL data at the input, and when coupled to the data bus with a 1:1 transformer, isolated on the transceiver side with two 35 Ohm fault isolation resistors, and loaded by a 170 Ohm termination, the data bus signal produced is 20 volts nominal P-P at A-A'. (See Figure 5.) When both DATA and DATA inputs are held low or high, the transmitter output impedance is low, and signal is "removed" from the line. In addition,