Industrielle styresystemer - Wiki
The task is to establish data exchange between 2 PLCs.
There are 2 main ways to exchange data: NVL and Modbus TCP.
Below are tables of advantages and disadvantages of these two methods, however, the biggest difference lies in which data transmission protocol is used.
TCP vs UDP: Differences between the protocols. The main difference between TCP (transmission control protocol) and UDP (user datagram protocol) is that TCP is a connection-based protocol and UDP is connectionless. While TCP is more reliable, it transfers data more slowly. UDP is less reliable but works more quickly.
NVL or Network Variables List
https://help.codesys.com/api-content/2/codesys/3.5.13.0/en/_cds_f_networkvariables/
| Advantages | Disadvantages |
|---|---|
| Easy to use | Uses UDP protocol, UDP provides a simpler and less reliable form of data transmission |
| Data transmission efficiency: NVL sends data in packets | Delivery is not guaranteed |
| Absence of a main node: NVL does not have a binding to a main or subordinate node, making it more flexible in usage and management | Only UDP protocol or it's limited protocol support |
| Optional data reading: Since data can be available to all nodes, there is no guarantee that all nodes will read or use this data |
Modbus TCP
| Advantages | Disadvantages |
|---|---|
| Reliability: Modbus TCP protocol ensures reliable data transmission with acknowledgment of receipt | Use of master and slave in data transmission |
| Wide support | Limited data transmission speed: More complex data transmission protocol. |
| Delivery is guaranteed |
Since we are simulating the use of a bridge panel, we need to use TCP protocol for reliable data transmission.
PLC1 is 158.38.140.56. It will be a master.
PLC2 is 158.38.140.57. It will be a slave.
According to the task we need to transmit data of INT and BOOL types.
Since Modbus only supports WORD data transfer, we still can transfer our data.
For transmitting BOOL data, it's possible to use one bit from a 16-bit word register. As for INT data (integer numbers), they can also be transmitted via Modbus TCP by placing them in two consecutive 16-bit word registers.
Source:/Helpful links:
Configuring a Network Variable Exchange:
https://help.codesys.com/api-content/2/codesys/3.5.13.0/en/_cds_configuring_network_variables_exchange/
Modbus TCP:
https://www.prosoft-technology.com/kb/assets/intro_modbustcp.pdf
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