74HCT157
http://onsemi.com
5
PIN DESCRIPTIONS
INPUTS
A0, A1, A2, A3 (Pins 2, 5, 11, 14)
Nibble A inputs. The data present on these pins is
transferred to the outputs when the Select input is at a low
level and the Output Enable input is at a low level. The data
is presented to the outputs in noninverted form.
B0, B1, B2, B3 (Pins 3, 6, 10, 13)
Nibble B inputs. The data present on these pins is
transferred to the outputs when the Select input is at a high
level and the Output Enable input is at a low level. The data
is presented to the outputs in noninverted form.
OUTPUTS
Y0, Y1, Y2, Y3 (Pins 4, 7, 9, 12)
Data outputs. The selected input Nibble is presented at
these outputs when the Output Enable input is at a low level.
The data present on these pins is in its noninverted form. For
the Output Enable input at a high level, the outputs are at a
low level.
CONTROL INPUTS
Select (Pin 1)
Nibble select. This input determines the data word to be
transferred to the outputs. A low level on this input selects
the A inputs and a high level selects the B inputs.
Output Enable (Pin 15)
Output Enable input. A low level on this input allows the
selected input data to be presented at the outputs. A high
level on this input sets all outputs to a low level.
SWITCHING WAVEFORMS
INPUT A OR B
OUTPUT
ENABLE
t
PLH
t
PHL
t
r
t
f
V
CC
GND
t
THL
t
TLH
10%
50%
90%
10%
50%
90%
OUTPUT Y
*Includes all probe and jig capacitance
C
L
*
TEST POINT
DEVICE
UNDER
TEST
OUTPUT
t
r
t
f
V
CC
GND
OUTPUT Y
t
PHL
t
PLH
10%
50%
90%
10%
50%
90%
t
TLH
t
THL
t
r
t
f
V
CC
GND
SELECT
OUTPUT Y
t
PHL
t
PLH
t
TLH
t
THL
10%
50%
90%
10%
50%
90%
Figure 3. HCT157 Figure 4. Y versus Selected, Noninverted
Figure 5. HCT157
Figure 6. Test Circuit
