The SN54/74LS85 is a 4-bit Magnitude Camparator that compares two 4-bit words (A, B), each word having four Parallel Inputs (A0–A3, B0–B3); A3, B3 being the most significant inputs. Operation is not restricted to binary codes, the device will work with any monotonic code. Three Outputs are provided: “A greater than B” (OA>B), “A less than B” (OA<B), “A equal to B” (OA=B). Three Expander Inputs, IA>B, IA<B, IA=B, allow cascading without external gates. For proper compare operation, the Expander Inputs to the least significant position must be connected as follows: IA<B= IA>B = L, IA=B = H. For serial (ripple) expansion, the OA>B, OAB, IA<B, and IA=B Inputs of the next most significant comparator, as shown in Figure 1. Refer to the Applications section of the datasheet for the high-speed method of comparing large words. The Truth Table on the following page describes the operation of the SN54/74LS85 under all possible logic conditions. The upper 11 lines describe the normal operation under all conditions that will occur in a single device or a series expansion scheme. The lower five lines describe the operation under abnormal conditions on the cascading inputs. These conditions occur when the parallel expansion technique is used.

Features

1. Easily Expandable
2. Binary or BCD Comparison
3. OA>B, OA<B, and OA=B Outputs Available