DS78LS120QML Datasheet, PDF (8/12 Pages) Texas Instruments – Dual Differential Line Receiver (Noise Filtering and Fail-Safe)

DS78LS120QML, DS78LS120
DS78LS120 is OBSOLETE
SNLS370C – SEPTEMBER 1999 – REVISED APRIL 2013
www.ti.com
For balanced operation with inputs open or shorted, receiver C will be in an indeterminate logic state. Receivers
A and B will be in a logic zero state allowing the NOR gate to detect the open or short condition. The strobe will
disable receivers A and B and may therefore be used to sample the fail-safe detector. Another method of fail-
safe detection consists of filtering the output of NOR gate D so it would not indicate a fault condition when
receiver inputs pass through the threshold region, generating an output transient.
In a communications system, only the control signals are required to detect input fault conditions. Advantages of
a balanced data transmission system over an unbalanced transmission system are:
1. High noise immunity
2. High data ratio
3. Long line lengths
Truth Table
(For Balanced Fail-Safe)
Input
Strobe
A-Out
0
1
0
1
1
1
X
1
0
0
0
1
1
0
1
X
0
1
B-Out
1
0
0
1
1
1
C-Out
0
1
X
0
0
0
Schematic Diagram
D-Out
0
0
1
0
0
0
8
Submit Documentation Feedback
Copyright © 1999–2013, Texas Instruments Incorporated
Product Folder Links: DS78LS120QML DS78LS120