DM74LS85 4-Bit Magnitude Comparator
August 1986 Revised March 2000
DM74LS85 4-Bit Magnitude Comparator
General Description
These 4-bit magnitude comparators perform comparison of straight binary or BCD codes. 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 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 inputs of the next stage handling more-significant bits. The stage handling the leastsignificant bits must have a high-level voltage applied to the A = B input. The cascading path is implemented with only a two-gate-level delay to reduce overall comparison times for long words.
Features
s Typical power dissipation 52 mW s Typical delay (4-bit words) 24 ns
Ordering Code:
Order Number DM74LS85M DM74LS85N Package Number M16A N16E Package Description 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram
© 2000 Fairchild Semiconductor Corporation
DS006379
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DM74LS85
Function Table
Comparing Inputs A3, B3 A3 > B3 A3 < B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A3 = B3 A2, B2 X X A2 > B2 A2 < B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A2 = B2 A1, B1 X X X X A1 > B1 A1 < B1 A1 = B1 A1 = B1 A1 = B1 A1 = B1 A1 = B1 A1 = B1 A1 = B1 A1 = B1 A0, B0 X X X X X X A0 > B0 A0 < B0 A0 = B0 A0 = B0 A0 = B0 A0 = B0 A0 = B0 A0 = B0 A>B X X X X X X X X H L L X H L Cascading Inputs A
B H L H L H L H L H L L L L H AB Others AB Others AB Others −20 10 2.7 3.4 0.35 0.25 0.5 0.4 0.1 0.1 0.3 20 20 60 −0.4 −0.4 −1.2 −100 20 mA mA mA µA mA Min Typ (Note 2) Max −1.5 Units V V
V
Note 2: All typicals are at VCC = 5V, TA = 25°C. Note 3: Not more than one output should be shorted at a time, and the duration should not exceed one second. Note 4: ICC is measured with all outputs OPEN, A = B grounded and all other inputs at 4.5V.
3
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DM74LS85
Switching Characteristics
at VCC = 5V and TA = 25°C From Symbol Parameter Input To Output A < B, A>B A=B tPHL Propagation Delay Time HIGH-to-LOW Level Output tPLH tPHL tPLH tPHL tPLH tPHL Propagation Delay Time LOW-to-HIGH Level Output Propagation Delay Time HIGH-to-LOW Level Output Propagation Delay Time LOW-to-HIGH Level Output Propagation Delay Time HIGH-to-LOW Level Output Propagation Delay Time LOW-to-HIGH Level Output Propagation Delay Time HIGH-to-LOW Level Output Any A or B Data Input A < B, A>B A=B A < B or A = B A < B or A = B A=B A=B A > B or A = B A > B or A = B A>B A>B A=B A=B A