5-172

FAST AND LS TTL DATA

SN54/74LS95B

LOGIC DIAGRAM

Q0

Q1

Q2

Q3

S

DS

CP1

CP2

P0

P2

P3

R

S

Q

P1

R

S

Q

R

S

Q

R

S

Q

VCC = PIN 14

GND = PIN 7

= PIN NUMBERS

6

1

2

3

8

4

5

9

11

12

10

13

FUNCTIONAL DESCRIPTION

The LS95B is a 4-Bit Shift Register with serial and parallel

synchronous operating modes. It has a Serial (DS) and four

Parallel (P0–P3) Data inputs and four Parallel Data outputs

(Q0–Q3). The serial or parallel mode of operation is controlled

by a Mode Control input (S) and two Clock Inputs (CP1) and

(CP2). The serial (right-shift) or parallel data transfers occur

synchronous with the HIGH to LOW transition of the selected

clock input.

When the Mode Control input (S) is HIGH, CP2 is enabled. A

HIGH to LOW transition on enabled CP2 transfers parallel

data from the P0–P3 inputs to the Q0–Q3 outputs.

When the Mode Control input (S) is LOW, CP1 is enabled. A

HIGH to LOW transition on enabled CP1 transfers the data

from Serial input (DS) to Q0 and shifts the data in Q0 to Q1, Q1

to Q2, and Q2 to Q3 respectively (right-shift). A left-shift is ac-

complished by externally connecting Q3 to P2, Q2 to P1, and

Q1 to P0, and operating the LS95B in the parallel mode (S =

HIGH).

For normal operation, S should only change states when

both Clock inputs are LOW. However, changing S from LOW

to HIGH while CP2 is HIGH, or changing S from HIGH to LOW

while CP1 is HIGH and CP2 is LOW will not cause any changes

on the register outputs.

MODE SELECT — TRUTH TABLE

OPERATING MODE

INPUTS

OUTPUTS

OPERATING MODE

S

CP1

CP2

DS

Pn

Q0

Q1

Q2

Q3

Shift

L

X

I

X

L

q0

q1

q2

Shift

L

X

h

X

H

q0

q1

q2

Parallel Load

H

X

X

Pn

P0

P1

P2

P3

L

L

X

X

No Change

L

L

X

X

No Change

H

L

X

X

No Change

Mode Change

H

L

X

X

Undetermined

L

H

X

X

Undetermined

L

H

X

X

No Change

H

H

X

X

Undetermined

H

H

X

X

No Change

L = LOW Voltage Level

H = HIGH Voltage Level

X = Don’t Care

I = LOW Voltage Level one set-up time prior to the HIGH to LOW clock transition.

h = HIGH Voltage Level one set-up time prior to the HIGH to LOW clock transition.