Bi-directional bus repeater

DETAILED DESCRIPTION In accordance with one aspect of the invention, a bi-directional bus repeater includes two unidirectional bus repeaters connected for retransmitting logic signals in opposite directions between two buses.
In a quiescent state when no external bus drivers are actively pulling down on the buses, small trickle currents supplied by the bus repeaters pull their output buses up to a high logic level.
When an external bus driver connected to either of the buses pulls that bus low, one of the unidirectional bus repeaters pulls the other bus low.
When the external bus driver releases the bus, allowing the bus to rise to a high logic state, the unidirectional bus repeater that was holding the other bus low responds by temporarily supplying a high charging current to the other bus to pull it quickly back up to the high logic level.
Thereafter the trickle currents continue to hold the other bus high.
Each unidirectional bus repeater also generates PULL UP and PULL DOWN signals indicating when the bus repeater is actively pulling up or down on a bus and the indicating signals produced by each unidirectional bus repeater are supplied as inputs to the other unidirectional bus repeater.
The indicating signal input inhibits one unidirectional bus repeater from actively driving its output bus up or down when the other bus repeater is actively driving its output bus up or down.
Thus the first unidirectional bus repeater to sense its input has been pulled down pulls down its output and inhibits the remaining unidirectional bus repeater from actively driving its output.
The first unidirectional bus repeater continues to inhibit the other until the first unidirectional bus repeater has stopped driving its output bus.
It is accordingly an object of the invention to provide an improved bi-directional bus repeater that automatically retransmits signals in both directions between two buses without need of an externally generated control signal for indicating the signal transmission direction