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RS485 Transparent Transmission allows supported WisNode Bridge devices to forward raw RS485 data over LoRaWAN® without application-layer parsing or conversion.

This is useful when the application server needs to process the original RS485 or Modbus data directly, or when the connected device uses a protocol that should remain unchanged during transmission.

The feature supports two transparent transmission modes:

• Polling Transparent Mode: The Bridge device actively polls RS485 devices according to configured polling tasks and forwards the returned raw Modbus data without parsing.
• Passive Transparent Mode: The Bridge device does not initiate Modbus polling. It forwards received RS485 data directly over LoRaWAN and forwards LoRaWAN downlink data directly to the RS485 interface.

Supported Devices

The following devices support RS485 Transparent Transmission:

Device	Polling Transparent Mode	Passive Transparent Mode
RAK2461 WisNode Bridge IO Lite	Supported	Supported
RAK2470 WisNode Bridge Serial Prime	Supported	Supported

NOTE

Product-specific interface behavior may vary. Refer to the corresponding product documentation for hardware interfaces and other functions available on your device.

Transmission Mode Overview

The RS485 Transmission Mode determines how received RS485 data is processed before it is sent over LoRaWAN.

Mode	Polling Task	Data Parsing	LoRaWAN Uplink
Parsing Mode	Required	Yes	Parsed structured data
Polling Transparent Mode	Required	No	Raw Modbus response data
Passive Transparent Mode	Not required	No	Raw RS485 data

Use:

• Parsing Mode when the Bridge device should parse Modbus responses and convert them into structured LoRaWAN payloads.
• Polling Transparent Mode when the Bridge device should actively query RS485 devices but the application server needs the original response data.
• Passive Transparent Mode when the Bridge device should act as a bidirectional transparent bridge without Modbus polling.

NOTE

Only one RS485 transmission mode can operate at a time.

Polling Transparent Mode

Configure Polling Transparent Mode

1. In IO.Box, go to RS485.
2. Configure the RS485 communication parameters to match the connected device.
3. Set Transmission Mode to Polling Transparent Mode.
   Figure 1: Polling Transparent
   NOTE

   The Max Payload Size is determined automatically according to the configured LoRaWAN region and DataRate.

4. Create the required Modbus Polling Tasks according to the RS485 device specification.
   Figure 1: Polling Task
5. Use Check to validate communication with the connected device.
6. Save the polling task when the returned data is correct.

Uplink Behavior

For each polling task, the Bridge device:

1. Sends the configured Modbus request to the RS485 device.
2. Receives the Modbus response.
3. Forwards the raw response data over LoRaWAN without converting it into structured sensor values.

Downlink Behavior

Polling Transparent Mode also supports sending a Modbus request from the LoRaWAN Network Server to the connected RS485 device.

Use FPort 130 for Polling Transparent Mode downlink data.

The downlink payload should contain the Modbus command without the CRC. The Bridge device automatically appends the Modbus CRC before transmitting the request through the RS485 interface.

For example, to read one holding register starting from register address 0x0000 on Modbus device address 0x01, send:

01 03 00 00 00 01

The payload contains:

• 01: Modbus device address
• 03: Read Holding Registers
• 00 00: Starting register address
• 00 01: Number of registers to read

Passive Transparent Mode

Configure Passive Transparent Mode

1. In IO.Box, go to RS485.
2. Set Transmission Mode to Passive Transparent Mode.
   Figure 1: Passive Transparent
   NOTE

   The Max Payload Size is determined automatically according to the configured LoRaWAN region and DataRate.

3. Configure the RS485 communication parameters to match the connected RS485 device.

Uplink Behavior

When the Bridge device receives RS485 data, it collects the received data as an RS485 frame and forwards the raw data over LoRaWAN without application-layer parsing.

Downlink Behavior

Passive Transparent Mode supports forwarding downlink data from the LoRaWAN Network Server directly to the RS485 interface.

Use FPort 131 for transparent downlink data.

The Bridge device does not parse or interpret the payload. Construct the downlink payload according to the communication protocol of the connected RS485 device.