RS485 MODBUS Module 8AI
User Manual
3. Communication configuration
3.1. Grounding and shielding
In most cases, IO modules will be installed in an enclosure along with other
devices which generate electromagnetic radiation. Examples of these devices are relays
and contactors, transformers, motor controllers etc. This electromagnetic radiation can
induce electrical noise into both power and signal lines, as well as direct radiation into
the module causing negative effects on the system. Appropriate grounding, shielding
and other protective steps should be taken at the installation stage to prevent these
effects. These protective steps include control cabinet grounding, module grounding,
cable shield grounding, protective elements for electromagnetic switching devices,
correct wiring as well as consideration of cable types and their cross sections.
3.2. Network Termination
Transmission line effects often present a problem on data communication
networks. These problems include reflections and signal attenuation.
To eliminate the presence of reflections from the end of the cable, the cable must
be terminated at both ends with a resistor across the line equal to its characteristic
impedance. Both ends must be terminated since the direction of propagation is bi-
directional. In the case of an RS485 twisted pair cable this termination is typically
120 Ω.
3.3. Setting Module Address in RS485 Modbus Network
The following table shows how to set switch to determine the address of the
module. The module address is set with the switches in the range of 0 to 31. Addresses
From 32 to 255 can by set via RS485 or USB.
Addr SW5 SW4 SW3 SW2 SW1
0
OFF OFF OFF OFF OFF
1
OFF OFF OFF OFF ON
2
OFF OFF OFF ON OFF
3
OFF OFF OFF ON
ON
4
OFF OFF
ON OFF OFF
5
OFF OFF
ON OFF ON
6
OFF OFF
ON
ON OFF
7
OFF OFF
ON
ON
ON
8
OFF ON
OFF OFF OFF
9
OFF ON
OFF OFF ON
10
OFF ON
OFF ON OFF
Addr SW5 SW4 SW3 SW2 SW1
11
OFF ON
OFF ON
ON
12
OFF ON
ON OFF OFF
13
OFF ON
ON OFF ON
14
OFF ON
ON
ON OFF
15
OFF ON
ON
ON
ON
16
ON OFF OFF OFF OFF
17
ON OFF OFF OFF ON
18
ON OFF OFF ON OFF
19
ON OFF OFF ON
ON
20
ON OFF
ON OFF OFF
21
ON OFF
ON OFF ON
Addr SW5 SW4 SW3 SW2 SW1
22
ON OFF
ON
ON OFF
23
ON OFF
ON
ON
ON
24
ON
ON
OFF OFF OFF
25
ON
ON
OFF OFF ON
26
ON
ON
OFF ON OFF
27
ON
ON
OFF ON
ON
28
ON
ON
ON OFF OFF
29
ON
ON
ON OFF ON
30
ON
ON
ON
ON OFF
31
ON
ON
ON
ON
ON
Expansion Module – 8 analog inputs
User Manual
Version 1.5
6 / 15
