M74HC181 Datasheet, PDF (2/13 Pages) STMicroelectronics – ARITHMETIC LOGIC UNIT/FUNCTION GENERATOR

M74HC181
DESCRIPTION (continued)
in the subtract mode with C_n = H when performing this
comparison. The A = B output is open-drain so that it
can be wire-AND connected to give a comparison for
more that four bits. The carry output (Cn + 4) can also
be used to supply relative magnitude information.
Again, the ALU should be placed in the subtract mode
by placing the function select inputs S3, S2, S1, S0 at
L, H, H, L, respectively. These circuits have been de-
signed to not only incorporate all of the designer’s re-
quirements for arithmetic operations, but also to pro-
vide 16 possible functions of two Boolean variables
without the use of external circuitry. These logic func-
tions are selected by use of the four function-select in-
puts (S0, S1, S2, S3) with the mode-control input (M)
at a high level to disable the internal carry. All inputs
are equipped with protection circuits against static dis-
charge and transient excess voltage.
INPUT AND OUTPUT EQUIVALENT CIRCUITS
ONLY OUTPUT A = B
IEC LOGIC SYMBOLS
PIN DESCRIPTION
PIN No
2, 23, 21, 19
1, 22, 20, 18
6, 5, 4, 3
7
8
9, 10, 11, 13
14
15
16
17
12
24
SYMBOL
A0 to A3
B0 to B3
S0 to S3
Cn
M
F0 to F3
A=B
P
Cn + 4
G
GND
V_CC
NAME AND FUNCTION
Word A Inputs
Word B Inputs
Function Select Inputs
Inv. Carry Input
Mode Control Input
Function Outputs
Comparator Output
Carry Propagate Output
Inv. Carry Output
Carry Generate Output
Ground (0V)
Positive Supply Voltage
PIN NUMBER
2 1 23 22 21 20 19 18 9 10 11 13 7 16 15 17
ACTIVE LOW DATA (Table 1) A0 B0 A1 B1 A2 B2 A3 B3 F0 F1 F2 F3 Cn Cn + 4 P G
ACTIVE HIGH DATA (Table 1) A0 B0 A1 B1 A2 B2 A3 B3 F0 F1 F2 F3 Cn Cn + 4 X Y
Input Cn
H
H
L
L
Output Cn + 4
H
L
H
L
Active LOW Data (Figure 1)
A≥B
A<B
A>B
A≤B
Active HIGH Data (Figure 2)
A≤B
A>B
A<B
A≥B
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