It is another object of the present invention to provide a multi-stage analog bi-directional selector that is low in cost. It is another object of the present invention to provide a multi-stage analog bi-directional selector that has a low impedance. It is accordingly an object of the present invention to provide a multi-stage analog bi-directional selector. The multi-stage analog bi-directional selector includes a plurality of analog switches including first and second bi-polar transistors coupled together at first and second connection points, a primary channel coupled to the first connection points, a plurality of data channels coupled to the second connection points, and an address circuit which causes a single one of the analog switches to form a bi-directional analog data connection between a corresponding single one of the data channels and the primary channel. In accordance with the teachings of the present invention, a multi-stage analog bi-directional selector is provided. Therefore, it would be desirable to provide a multi-stage analog bi-directional selector with low impedance and with low cost. The invention would be used in the keyboard to control placement of data from the wedged device onto the keyboard's communication channel. The computer may then choose which keyboard to communicate with.Īnother application for this invention is in keyboard wedge devices, in which communication with the wedged device would occur through the keyboard's communication interface. Thus, two keyboards may be more easily connected to a single keyboard controller 49 within a computer. Such a combination would be desirable, particularly for passing bi-directional TTL logic signals on a wire-or bus typical of what is found in the PC-AT keyboard, namely clock and data signals. Presently, there are no low impedance devices which combine the data path selection of a multiplexer with the asynchronous bi-directional communication of an analog switch. This impedance requires a proportional increase in the voltage of the circuit which drives such a switch. They also have input impedances which are too high (about 200 ohms maximum). Multiplexers and de-multiplexers perform data path selection, but do not support asynchronous bi-directional communication.Īnalog switches control bi-directional communication, but do not support data path selection. The present invention relates to communication switching circuitry, and more specifically to a multi-stage analog bi-directional selector.

Transistor keyboard or controller