Settings
Settings define how the device communicates on the Modbus RTU serial line. They control device identification, communication timing, error handling, and how multi‑register values are interpreted.
Correct settings are required for stable communication and compatibility with the Anybus SoM.
Modbus Node ID
The Modbus Node ID identifies the device on the serial line. Each device on the bus must have a unique Node ID so requests are addressed correctly.
Valid range: 0–255
Default value: 1
Required: Yes
Note
Node ID 0 is the Modbus broadcast address and is processed by all devices on the bus. Use it only for specific broadcast operations.
Note
Node IDs 248–255 are reserved by the Modbus specification and must not be used for normal device addressing.
Register order
Register order defines how multi‑register values, such as UINT32 and FLOAT64, are stored and interpreted.
This setting applies to:
Holding registers
Input registers
Multi‑register values for Coils and Discrete inputs always use most significant register first and are not affected by this setting
Supported register orders
Most significant register first (default)
Least significant register first
Byte order
Byte order within each 16‑bit register is always big endian and cannot be changed.
Bitrate (bps)
The bitrate defines the communication speed of the Modbus RTU connection.
The selected bitrate must be supported by both the Modbus server and the Anybus SoM to ensure reliable communication.
Default: 19 200 bits per second (bps)
When selecting the bitrate, consider:
Size of the transferred data sets
Required minimum network cycle time
Note
A bitrate that is too low may prevent all required data from being transferred within the desired cycle time.
Parity and stop bits
Parity and stop bits define the Modbus RTU frame format.
Use the same parity and stop‑bit settings as the Modbus server.
Mismatched settings are a common cause of communication errors.
Default: E1 (Even parity, 1 stop bit)
Parity
Parity provides basic error checking.
Value | Description |
|---|---|
None (N) | No error checking |
Odd (O) | Ensures an odd number of 1‑bits |
Even (E) | Ensures an even number of 1‑bits |
Stop bits
Stop bits mark the end of each transmitted byte.
Value | Description |
|---|---|
1 stop bit | One stop bit is transmitted |
2 stop bits | Two stop bits are transmitted |
Timeout (ms)
The timeout specifies how long the device waits for a response before marking a request as failed.
Valid range: 0–65 535 ms
Default: 1000 ms
Required: Yes
Timeouts best practices
Use shorter timeouts in fast systems.
Use longer timeouts in slow or noisy serial environments.
Retries
Retries define how many times a failed request is repeated.
Valid range: 0–255
Default: 2
Required: Yes
Retires best practices
Use low retry values for fast fault detection.
Use higher values in noisy serial environments.