Bi-directional keyboard interface circuit

摘要

The present invention includes a keyboard encoder which encodes a key selected by an operator. The encoder is isolated from a bi-directional bus by an isolation circuit. When a key has been selected a key code is made available for reading by a separate CPU. The separate CPU enables transfer of the key code from the encoder to the bi-directional bus and then reads the key code. The separate CPU acknowledges receipt of the key code and provides feedback to keyboard operator by sending a bank and light selection code to the keyboard over the bi-directional interface bus, after the isolation circuit has been reactivated and after a function, to be performed by the separate CPU and specified by the key code, has been started. The isolation circuit prevents the key code and the bank and light selection code from becoming intermixed on the bi-directional bus. The bank select code is used to select a bank of light code decoders which activate a light corresponding to the light code. The light activated stays lit until another key is selected. The transmission of a second bank and light selection code after a single key is selected can be used to activate an additional light associated with the selected key.