Module for a serial multiplex data input protection circuit

In a data ink module having an integrated circuit with an data bus terminal for receipt of digital data signals from a data bus, a local input terminal for receipt of input signals from a local input device, and a time division multiplexing address defining one of a plurality of time slots between synchronization pulses, a high voltage protection circuit, comprising:

• a switchable breakdown device with an input junction and a pair of transconductive outputs and having a breakdown voltage at which a short is created between the transconductive outputs;
• means for connecting one of the transconductive outputs to a data bus susceptible to voltage spikes in excess of the breakdown voltage and detrimental to the integrated circuit if applied to the input;
• means for connecting the other transconductive output to a reference potential;
• and
• means responsive to the address and to the signals at at least one of the local input terminal and the data bus terminal to provide a drive signal to the input junction of the switchable breakdown device to provide an appropriate data signal on the data bus during the time slot of the address of the data link module, said switchable breakdown device breaking down to protect the integrated circuit from said voltage spikes when not being driven to provide data signals to the data bus.