Selecting The Reference Point Of The Protection Circuitry; Serial Port 1; Serial Port 2; Fig. 8-17: Selecting The Reference Point Of The Protection Circuitry (Serial Port 1) - Addi-Data ADDICOM PA 7400 Series Technical Description

Technical description

8.3.5 Selecting the reference point of the protection circuitry

On serial ports 1 and 2 the input and output lines are protected against
overvoltage directly behind the peripheral connector through damping diodes.
- RS 422, RS 485 and 20mA current loop (optically isolated)
- RS 422 and RS 485
The protection circuitry is composed of TRANSIL damping diodes on all lines.
Breakdown voltage = ± 6.5V
All the lines are protected against short-circuit through positive temperature
coefficient resistors.
- 20mA current loop
The current loops are protected with TRANSIL damping diodes.
Breakdown voltage: ± 26V

Serial port 1

•
Select the reference point of the protection circuitry through jumper J24.
IMPORTANT!
Make sure that pin 1 of the 25-pin SUB-D connector is earthed
externally.
Fig. 8-17: Selecting the reference point of the protection circuitry
If pin 1 of the 25-pin SUB D connector is used for derivating noise voltage,
•
connect pin 1 of the connection cable
- with the cable shield as well as
- with the housing of the female connector fixed to the cable.

Serial port 2

•
Select the reference point of the protection circuitry through jumper J5.
Chapter 8
(serial port 1)
PA 7400
45