Patent ID: 7417464

Claim:
A bi-directional signal transmission system including; a first bi-directional signal path having circuitry adapted to generate a logic high level on said first path, one or more first stations connected to the first bi-directional signal path adapted to monitor a logic level on said first path, and to generate a logic low level on said first path; an interface device operatively coupled to the first bi-directional signal path, said interface device having a first receive input also capable of functioning as an output capable of pulling the first path low; and a second bi-directional signal path coupled to a transmit output and a receive input on the buffered side of the interface device, said interface device includes a first means for generating on the first bi-directional signal path a medium logic level in response to a low level on the receive input on the buffered side, and a second means for generating on the transmit output on the buffered side, a low logic level in response to a low level on the first bi-directional signal path, otherwise generating a high level on the said transmit output, wherein the one or more first stations are adapted to detect the medium and the low levels on the first bi-directional signal path as LOW, and the high logic level on the first bi-directional signal path as HIGH, and wherein further the first means for generating the medium logic level on the first signal path includes an open collector transistor, the emitter of which is connected to VEE, with its collector pulling the first signal path low through a diode connected transistor.