Fairchild Semiconductor DM74LS85N, DM74LS85MX, DM74LS85M Datasheet

© 2000 Fairchild Semiconductor Corporation DS006379 www.fairchildsemi.com

August 1986
Revised March 2000

DM74LS85 4-Bit Magnitude Comparator

DM74LS85
4-Bit Magnitude Comparator

General Description

These 4-bit magnitude comparators perform comparison of
straight binary or BCD cod es. Three fully-decoded deci­sions about two, 4-bit words (A, B) are made and are exter­nally available at three outputs. These devices are fully
expandable to any nu mber of bits without ex ternal gates.
Words of greater length may be compa red by connecting
comparators in cascade. The A > B, A < B, a nd A = B out­puts of a stage handlin g l e ss-sig nifi ca nt b its a re connected
to the corresponding inputs of the next stage handling
more-significant bits. The stage handling the least­significant bits must ha ve a high-level voltage applied to
the A = B input. The cascading path is implem ented with
only a two-gate-level delay to reduce overall compar ison
times for long words.

Features

■ Typical power dissipation 52 mW

■ Typical delay (4-bit words) 24 ns

Ordering Code:

Devices also availab le in Tape and Reel. Specify by appending th e s uffix let t er “X” to the ordering code.

Connection Diagram

Order Number Package Number Package Description

DM74LS85M M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
DM74LS85N N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide

www.fairchildsemi.com 2

DM74LS85

Function Table

H = HIGH Level, L = LOW Level, X = Don’t Care

Logic Diagram

Comparing Cascading Outputs

Inputs Inputs

A3, B3 A2, B2 A1, B1 A0, B0 A > BA < BA = BA > BA < BA = B

A3 > B3X X X XXXHLL
A3 < B3X X X XXXLHL
A3 = B3 A2 > B2X X XXXHLL
A3 = B3 A2 < B2X X XXXLHL
A3 = B3 A2 = B2 A1 > B1X XXXHLL
A3 = B3 A2 = B2 A1 < B1X XXXLHL
A3 = B3 A2 = B2 A1 = B1 A0 > B0XXXHLL
A3 = B3 A2 = B2 A1 = B1 A0 < B0XXXLHL
A3 = B3 A2 = B2 A1 = B1 A0 = B0 H L L H L L
A3 = B3 A2 = B2 A1 = B1 A0 = B0 L H L L H L
A3 = B3 A2 = B2 A1 = B1 A0 = B0 L L H L L H
A3 = B3 A2 = B2 A1 = B1 A0 = B0 X X H L L H
A3 = B3 A2 = B2 A1 = B1 A0 = B0HHLLLL
A3 = B3 A2 = B2 A1 = B1 A0 = B0LLLHHL