FMS Integration shows how to wire modbus RS485 serial communications for Modbus serial communications.
FMS shows two examples an RS485 2-wire and an RS485 4-wire connection.
We use a MOXA Mgate MB3170, capable of a 2-wire or 4-wire connection type. The MOXA Mgate family of products can also have multiple baud rate options. None, even or odd parity settings, and selectable stop bits.
Wiring Modbus RS485 communications involves connecting the devices in a daisy-chain or multi-drop configuration using twisted pair cables. Here's a step-by-step guide on how to wire Modbus RS485 communications:
1. Gather the necessary materials:
- Modbus RS485 devices (such as PLCs, sensors, or meters) that support RS485 communication.
- Twisted pair cables (usually two wires) with appropriate gauge and shielding.
- RS485 terminators (optional, depending on the network topology).
2. Determine the network topology:
- Modbus RS485 networks can be set up in two common configurations: daisy-chain and multi-drop.
- Daisy-chain configuration: All devices are connected in a linear fashion, with each device connected to the next one.
- Multi-drop configuration: All devices are connected in parallel, with a common bus shared by all devices.
3. Connect the devices:
- Start by identifying the Modbus RS485 ports on each device. They are usually labeled as "A" and "B" or "Positive" and "Negative."
- For the daisy-chain configuration:
- Connect the "A" terminal of the first device to the "B" terminal of the second device using one twisted pair wire.
- Connect the "B" terminal of the first device to the "A" terminal of the second device using another twisted pair wire.
- Repeat this process for each device in the chain until all devices are connected.
- For the multi-drop configuration:
- Connect the "A" terminal of all devices together using one twisted pair wire.
- Connect the "B" terminal of all devices together using another twisted pair wire.
- This creates a common bus shared by all devices.
4. Add terminators (if required):
- In some cases, the RS485 network may require terminators to minimize signal reflections and improve communication reliability.
- For the daisy-chain configuration:
- Place a terminator at the last device in the chain by connecting a resistor between the "A" and "B" terminals.
- For the multi-drop configuration:
- Place a terminator at both ends of the common bus by connecting resistors between the "A" and "B" terminals.
5. Power the devices:
- Connect the power supply to each device according to the manufacturer's instructions.
- Ensure that the power supply voltage matches the device requirements.
6. Verify the wiring:
- Double-check all connections to ensure they are properly made.
- Ensure that the twisted pair cables are properly shielded and grounded.
- Confirm that the terminators (if used) are correctly placed.
Once the devices are wired, you can proceed with configuring the Modbus settings, such as the slave addresses and communication parameters (baud rate, parity, etc.), in each device to establish communication. Consult the documentation or user manuals of the specific devices you are using for detailed configuration instructions.
If you have an application you would like to discuss, please contact us at fmssi.com/contact
#moxa #modbus wiring #rs485
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