5-84
FAST AND LS TTL DATA
4-BIT MAGNITUDE
COMPARATOR
The SN54 / 74LS85 is a 4-Bit Magnitude Camparator which compares two
4-bit words (A, B), each word having four Parallel Inputs (A0A3, B0B3); 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, OA< B and OA= B Outputs are
connected respectively to the IA> B, IA< B, and IA= B Inputs of the next most
significant comparator, as shown in Figure 1. Refer to Applications section of
data sheet for 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
in 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.
Easily Expandable
Binary or BCD Comparison
OA> B, OA< B, and OA= B Outputs Available
CONNECTION DIAGRAM DIP (TOP VIEW)
NOTE:
The Flatpak version has the
same pinouts (Connection
Diagram) as the Dual In-Line
Package.
14
13
12
11
10
9
1
2
3
4
5
6
7
16
15
8
VCC
B3
A3
B2
A2
A1
A0
B1
B0
IA<B IA=B IA>B OA>B OA=B OA<B GND
PIN NAMES
LOADING (Note a)
HIGH
LOW
A0 A3, B0 B3
IA = B
IA < B, IA > B
OA > B
OA < B
OA = B
Parallel Inputs
A = B Expander Inputs
A < B, A > B, Expander Inputs
A Greater Than B Output (Note b)
B Greater Than A Output (Note b)
A Equal to B Output (Note b)
1.5 U.L.
1.5 U.L.
0.5 U.L.
10 U.L.
10 U.L.
10 U.L.
0.75 U.L.
0.75 U.L.
0.25 U.L.
5 (2.5) U.L.
5 (2.5) U.L.
5 (2.5) U.L.
NOTES:
a) 1 TTL Unit Load (U.L.) = 40
A HIGH/1.6 mA LOW.
b) The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74)
Temperature Ranges.
SN54/74LS85
4-BIT MAGNITUDE
COMPARATOR
LOW POWER SCHOTTKY
J SUFFIX
CERAMIC
CASE 620-09
N SUFFIX
PLASTIC
CASE 648-08
16
1
16
1
ORDERING INFORMATION
SN54LSXXJ
Ceramic
SN74LSXXN
Plastic
SN74LSXXD
SOIC
16
1
D SUFFIX
SOIC
CASE 751B-03
LOGIC SYMBOL
VCC = PIN 16
GND = PIN 8
10 12 13 15 9 11 14 1
4
2
3
5
7
6
A0 A1 A2 A3 B0 B1 B2 B3
IA>B
IA<B
IA=B
OA>B
OA<B
OA=B
NOTE:
The SN54/74LS85 can be used as a 5-bit comparator
only when the outputs are used to drive the A0A3 and
B0B3 inputs of another SN54/74LS85 as shown in
Figure 2 in positions #1, 2, 3, and 4.
5-86
FAST AND LS TTL DATA
SN54/74LS85
Figure 1. Comparing Two n-Bit Words
L = LOW LEVEL
H = HIGH LEVEL
A0 A1 A2 A3 B0 B1 B2 B3
A0 A1 A2 A3 B0 B1 B2 B3
A0 A1 A2 A3 B0 B1 B2 B3
L
L
H
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
A > B
A < B
A = B
SN54/74LS85
SN54/74LS85
A
n3
A
n2
A
n1
A
n
B
n3
B
n2
B
n1
B
n
APPLICATIONS
Figure 2 shows a high speed method of comparing two 24-bit words with only two levels of device delay. With the technique
shown in Figure 1, six levels of device delay result when comparing two 24-bit words. The parallel technique can be expanded
to any number of bits, see Table 1.
Table 1
WORD LENGTH
NUMBER OF PKGS.
1 4 Bits
1
5 24 Bits
2 6
25 120 Bits
8 31
MSB = MOST SIGNIFICANT BIT
LSB = LEAST SIGNIFICANT BIT
L = LOW LEVEL
H = HIGH LEVEL
NC = NO CONNECTION
A0 A1 A2 A3 B0 B1 B2 B3
A0 A1 A2 A3 B0 B1 B2 B3
L
L
H
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
#5
(LSB)
INPUTS
A0 A1 A2 A3 B0 B1 B2 B3
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
#1
L
NC
A20 A21
B23
B22
B21
B20
A23
A22
A19
B19
(MSB)
A5 A6 A7 A8 B5 B6 B7 B8
A0 A1 A2 A3 B0 B1 B2 B3
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
#4
NC
L
A4
B4
A0 A1 A2 A3 B0 B1 B2 B3
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
#3
NC
L
A9
B9
A10 A11
B13
B12
B11
B10
A13
A12
A0 A1 A2 A3 B0 B1 B2 B3
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
#2
NC
L
A14
B14
A15 A16
B18
B17
B16
B15
A18
A17
OUTPUTS
A0 A1 A2 A3 B0 B1 B2 B3
IA > B
IA < B
IA = B
OA > B
OA < B
OA = B
#6
INPUTS
Figure 2. Comparison of Two 24-Bit Words
5-87
FAST AND LS TTL DATA
SN54/74LS85
DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE
(unless otherwise specified)
Symbol
Parameter
Limits
Unit
Test Conditions
Symbol
Parameter
Min
Typ
Max
Unit
Test Conditions
VIH
Input HIGH Voltage
2.0
V
Guaranteed Input HIGH Voltage for
All Inputs
VIL
Input LOW Voltage
54
0.7
V
Guaranteed Input LOW Voltage for
All Inputs
VIL
Input LOW Voltage
74
0.8
V
Guaranteed Input LOW Voltage for
All Inputs
VIK
Input Clamp Diode Voltage
0.65
1.5
V
VCC = MIN, IIN = 18 mA
VOH
Output HIGH Voltage
54
2.5
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOH
Output HIGH Voltage
54
2.5
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOH
Output HIGH Voltage
74
2.7
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOL
Output LOW Voltage
54, 74
0.25
0.4
V
IOL = 4.0 mA
VCC = VCC MIN,
VIN = VIL or VIH
per Truth Table
VOL
Output LOW Voltage
74
0.35
0.5
V
IOL = 8.0 mA
VIN = VIL or VIH
per Truth Table
IIH
Input HIGH Current
A < B, A > B
Other Inputs
20
60
A
VCC = MAX, VIN = 2.7 V
IIH
A < B, A > B
Other Inputs
0.1
0.3
mA
VCC = MAX, VIN = 7.0 V
IIL
Input LOW Current
A < B, A > B
Other Inputs
0.4
1.2
mA
VCC = MAX, VIN = 0.4 V
IOS
Output Short Circuit Current (Note 1)
20
100
mA
VCC = MAX
ICC
Power Supply Current
20
mA
VCC = MAX
Note 1: Not more than one output should be shorted at a time, nor for more than 1 second.
AC CHARACTERISTICS
(TA = 25
C, VCC = 5.0 V)
Symbol
Parameter
Limits
Unit
Test Conditions
Symbol
Parameter
Min
Typ
Max
Unit
Test Conditions
tPLH
tPHL
Any A or B to A < B, A > B
24
20
36
30
ns
VCC = 5.0 V
CL = 15 pF
tPLH
tPHL
Any A or B to A = B
27
23
45
45
ns
VCC = 5.0 V
CL = 15 pF
tPLH
tPHL
A < B or A = B to A > B
14
11
22
17
ns
VCC = 5.0 V
CL = 15 pF
tPLH
tPHL
A = B to A = B
13
13
20
26
ns
tPLH
tPHL
A > B or A = B to A < B
14
11
22
17
ns
Figure 3
Figure 4
AC WAVEFORMS
VIN
VOUT
1.3 V
tPHL
1.3 V
1.3 V
1.3 V
tPLH
VIN
VOUT
1.3 V
tPHL
1.3 V
1.3 V
1.3 V
tPLH
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