Four-Input To Two-Bit Binary Priority Encoder

For the binary code and status output signals to function, nENIN (active low ENABLE INPUT) should be asserted. S0 to S3 are switches which when ON generates the active low signal to be encoded. S0 has the highest priority and S3 has the lowest priority. The pair of two-input NAND gates following the OR array generates the binary code corresponding to the switch pressed. The five-input NAND gate generates an active low ENABLE OUTPUT (/EO) status which is asserted when nENIN is active but all input switches are OFF. The lone two-input NAND gate at the top portion of the circuit generates an active low GROUP SELECT (/GS) status which is asserted when nENIN is active and at least one switch is ON.