SN74LS85D (TEXAS INSTRUMENTS)

The SN74LS85D is a 4-bit Magnitude Comparator performs comparison of straight binary and straight BCD (8-4-2-1) codes. Three fully decoded decisions about two 4-bit words (A, B) are made and are externally available at three outputs. It is fully expandable to any number of bits without external gates. Words of greater length may be compared by connecting comparators in cascade. The A >B, A <B and A = B outputs of a stage handling less-significant bits are connected to the corresponding A >B, A <B and A = B inputs of the next stage handling more-significant bits. The stage handling the least-significant bits must have a high-level voltage applied to the A = B input. The cascading path of the LS85 is implemented with only a two-gate-level delay to reduce overall comparison times for long words. An alternate method of cascading which further reduces the comparison time is shown in the typical application data.