MC74HC85 Datasheet, PDF (4/8 Pages) Motorola, Inc – 4-Bit Magnitude Comparator

MC74HC85
PIN DESCRIPTIONS
INPUTS
A0, A1, A2, A3 (Pins 10, 12, 13, 15)
Data Nibble A Inputs. The data nibble present at these in-
puts is compared to Data Nibble B. A3 is the most significant
bit and A0 is the least significant bit.
B0, B1, B2, B3 (Pins 9, 11, 14, 1)
Data Nibble B Inputs. The data nibble present at these in-
puts is compared to Data Nibble A. B3 is the most significant
bit and B0 is the least significant bit.
CONTROLS
A > Bin, A = Bin, A < Bin (Pins 4, 3, 2)
Cascading Inputs. These inputs determine the states of
the outputs only when Data Nibble A equals Data Nibble B.
The A = Bin input overrides both the A > Bin and A < Bin
inputs.
For single stage operation or for the least significant stage
in cascaded operation, the A < Bin and A > Bin inputs should
be tied to ground and the A = Bin input tied to VCC. Between
cascaded comparators, the A < Bout, A = Bout, and A > Bout
outputs should be tied to A < Bin, A = Bin, and A > Bin, re-
spectively, of the succeeding stage.
OUTPUTS
A > Bout (Pin 5)
A–Greater–Than–B Output. This output is at a high volt-
age level when Nibble A is greater than Nibble B, regardless
of the data present at the cascading inputs. This output is
also high when Nibble A equals Nibble B and the A > Bin in-
put is high (A < Bin and A = Bin are at a low voltage level).
A = Bout (Pin 6)
A–Equals–B Output. This output is high when Nibble A
equals Nibble B and the A = Bin input is high. A < Bin and
A > Bin have no effect when the comparator is in this condi-
tion and A = Bin is at a high voltage level.
A < Bout (Pin 7)
A–Less–Than–B Output. This output is at a high voltage
level when Nibble A is less than Nibble B, regardless of data
present at the cascading inputs. This output is also high
when Nibble A equals Nibble B and the A < Bin input is high
(A > Bin and A = Bin are at a low voltage level).
Data Inputs
A3, B3
A2, B2
A1, B1
A3 > B3
X
X
A3 < B3
X
X
A3 = B3 A2 > B2
X
A3 = B3 A2 < B2
X
A3 = B3
A3 = B3
A3 = B3
A3 = B3
A2 = B2
A2 = B2
A2 = B2
A2 = B2
A1 > B1
A1 < B1
A1 = B1
A1 = B1
A3 = B3
A3 = B3
A3 = B3
A3 = B3
A3 = B3
A2 = B2
A2 = B2
A2 = B2
A2 = B2
A2 = B2
A1 = B1
A1 = B1
A1 = B1
A1 = B1
A1 = B1
X = Don’t Care
FUNCTION TABLE
Cascading Inputs
A0, B0
X
X
X
X
A > Bin
X
X
X
X
A = Bin
X
X
X
X
A < Bin
X
X
X
X
X
X
X
X
X
X
X
X
A0 > B0
X
X
X
A0 < B0
X
X
X
A0 = B0
L
L
L
A0 = B0
L
L
H
A0 = B0
H
L
L
A0 = B0
H
L
H
A0 = B0
X
H
X
A > Bout
H
L
H
L
H
L
H
L
H
L
H
L
L
Output
A = Bout
L
L
L
L
L
L
L
L
L
L
L
L
H
A < Bout
L
H
L
H
L
H
L
H
H
H
L
L
L
MOTOROLA
4
High–Speed CMOS Logic Data
DL129 — Rev 6