DESCRIPTION
The HEF4585B is a 4-bit magnitude comparator which compares two 4-bit words (A and B), whether they are ‘less than’, ‘equal to’, or ‘greater than’. Each word has four parallel inputs (A0 to A3 and B0 to B3); A3 and B3 being the most significant inputs. Three outputs are provided; A greater than B (OA > B), A less than B (OA < B) and A equal to B (OA = B). Three expander inputs (IA > B, IA < B and IA = B) allow cascading of the devices without external gates.

For proper compare operation the expander inputs to the least significant position must be connected as follows: IA = B = IA > B = HIGH, IA < B = LOW. For words greater than 4-bits, units can be cascaded by connecting outputs OA < B and OA = B to the corresponding inputs of the next significant comparator (input IA > B is connected to a HIGH).

Operation is not restricted to binary codes, the devices will work with any monotonic code. The function table describes the operation of the device under all possible logic conditions.