MC74AC157, MC74ACT157
E I
0a
I
1a
I
0b
I
1b
I
0c
I
1c
I
0d
I
1d
S
Z
a
Z
b
Z
c
Z
d
Figure 2. Logic Symbol
FUNCTIONAL DESCRIPTION
The MC74AC157/74ACT157 is a quad 2−input
multiplexer. It selects four bits of data from two sources
under the control of a common Select input (S). The Enable
input (E) is active−LOW. When E is HIGH, all of the outputs
(Z) are forced LOW regardless of all other inputs. The
MC74AC157/74ACT157 is the logic implementation of a
4−pole, 2−position switch where the position of the switch
is determined by the logic levels supplied to the Select input.
The logic equations for the outputs are shown below:
Z
a
= E
•
(I
1a
•
S+I
0a
•
S)
Z
b
= E
•
(I
1b
•
S+I
0b
•
S)
Z
c
= E
•
(I
1c
•
S+I
0c
•
S)
Z
d
= E
•
(I
1d
•
S+I
0d
•
S)
A common use of the MC74AC157/74ACT157 is the
moving of data from two groups of registers to four common
output busses. The particular register from which the data
comes is determined by the state of the Select input. A less
obvious use is as a function generator. The
MC74AC157/74ACT157 can generate any four of the
sixteen different functions of two variables with one
variable common. This is useful for implementing gating
functions.
I
0a
I
1a
I
0b
I
1b
I
0c
I
1c
I
0d
I
1d
E
S
Z
a
NOTE:
Z
b
Z
c
Z
d
This diagram is provided only for the understanding of logic
operations and should not be used to estimate propagation delays.
Figure 3. Logic Diagram
http://onsemi.com
2
ONSEMI [ ON SEMICONDUCTOR ]
