How to choose among the three MODBUS communication methods?
Step 1: Check the physical interface first
- The device only has RS485/RS232 serial ports
Direct binary choice: RTU takes priority, ASCII serves as a special backup
- The device has a network port and needs to be connected to a switch/router/remote upload
Direct selection: Modbus TCP
Step 2: Select by distance
<1200 meters, workshop local wiring, twisted pair bus: RTU
Over 1200 meters, across workshops/cities/remote locations: TCP
Desktop short distance debugging only, old devices: ASCII
Step 3: Select by usage scenario
Required Modbus RTU
PLC connected to frequency converter, electricity meter, temperature controller, sensor, instrument, one master multiple slave bus network, saving wiring and switches
Industrial strong interference on site, requiring stability, reliable verification, low cost budget, and no need to add network ports and switches
Required Modbus TCP
To configure SCADA、 Cloud platforms, a large number of IoT devices, a large amount of data, and fast refresh rates are required
Need to cross network segments, remote access, and check the external network of mobile phones/computers. There are already Ethernet and LAN cables on site, and I don't want to install a separate 485 cable
Only select Modbus ASCII (limited to these two situations)
The old equipment on site only supports ASCII, so there is no need to choose serial port packet capture debugging. We need to check the plaintext message to troubleshoot the problem
Step 4: Quick Avoidance Rules
All new projects do not consider ASCII, it's useless and slow
Local close range device clustering → 485+RTU is the most cost-effective and stable option
To connect to the internet, remotely, and integrate with the upper computer system ->direct TCP
485 bus nodes exceed 32, with long distances and frequent lagging → Change to TCP networkingOne minute quick selection mnemonic
Local serial port 485, all use RTU; Network remote access to the system, directly select TCP; Use ASCII only for old devices and debugging messages.