Abstract: Keyboard coding apparatus couples to a plurality of keys and comprises a scanning interface including a counter (23), a decoder (13) and a multiplexer (22). The scanning interface, in response to each pulse received from a microprocessor (1) through an input lead (11), sends to the microprocessor on an output lead (10) a logic signal indicative of the state of any selected one of the keys. Whenever microprocessor 1 sends a pulse to the scanning interface, it increments by one the contents of an internal register and, before sending another pulse, processes the signal from the scanning interface. When the logic level of such signal indicates a condition of an actuated key, the microprocessor waits a predetermined time interval to establish that said selected key activation is valid, then waits until the selected key has been deactivated and then accesses the character code related to the actuated key from a memory location whose address is latched into its internal register.

Abstract: A system comprising several peripheral microprocessors are connected to a central processor through a common bus. Each processor may access the bus using an interrupt signal. In order to avoid conflicts among processors in accessing the bus, processors are designated with decreasing priority. A processor which accesses the bus by using said interrupt signal generates at the same time an inhibit signal which prevents processors having a lower priority from emitting a said interrupt signal. In order to reduce the propagation time, a bypass network for the inhibit signal is associated with each processor and a propagation path is provided for the inhibit signal in the form of a matrix.