74HC85; 74HCT85

The 74HC85; 74HCT85 is a 4-bit magnitude comparator that can be expanded to almost any length. They perform comparison of two 4-bit binary, BCD or other monotonic codes and present the three possible magnitude results at the outputs (Q_A>B, Q_A=B and Q_A<B). The 4-bit inputs are weighted (A0 to A3 and B0 to B3), where A3 and B3 are the most significant bits. For proper compare operation the expander inputs (I_A>B, I_A=B and I_A<B) to the least significant position must be connected as follows: I_A<B = I_A>B = LOW and I_A=B = HIGH. For words greater than 4-bits, units can be cascaded by connecting outputs Q_A>B, Q_A=B and Q_A<B to the corresponding inputs of the significant comparator. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of V_CC.