3.1 Modbus Master – configuration dialog
3.1.1 Modbus TCP/IP Master configuration
The configuration dialog is shown in Figure 3.1.
The upper left part of the dialog contains Connection parameters. Namely:
- Timeout
- – Maximal time in seconds to wait for the response from Slave station. The station is considered malfunctioning if no valid response is received. This parameter has no meaning for Slave variant of the driver.
- Reconnect
- – Interval for testing the malfunctioning stations (in seconds).
If the REX Control System acts as TCP/IP Master, it is necessary to define the Slave stations. The center part of dialog depicted in Fig. 3.1 displays the defined Slave stations. New Slave station can be added by pressing Add slave in the right column. Existing slaves can be edited directly in the Slave list or by pressing Edit slave button.
Following parameters define slave device:
- Name
- – A unique station name.
- Address
- – IP address of the Slave station.
- Port
- – Port (TCP address) of the Slave station. The default port for Modbus is 502.
- Max requests
- – Maximum number of Modbus telegrams in the queue. Especially the embedded devices with limited memory usually have a small TCP/IP stack buffer. The Master station tracks the requests and responses of each Slave station and postpones the requests if the Slave station fails to respond in a timely manner.
- Subaddress
- – Additional address field, values 1 to 255. The value of 255 is reserved for broadcast. Do not use 255 unless you have a special reason.
3.1.2 Modbus RTU Master configuration
The configuration dialog is shown in Figure 3.2.
The upper left part of the dialog contains Connection parameters. Namely:
- Port
- – The serial line used for communication. Usually COM* for Windows target devices or /dev/ttyS* for Linux target devices. Replace "*" symbol according to the chosen serial port!
- Baud rate
- – All stations on one bus must use the same baud rate. In bits per second.
- Parity
- – The error checking mechanism. All stations on one bus must use the same parity.
- Stopbit
- – Stop bits sent at the end of every character. All stations on one bus must use the same parity.
- Timeout
- – Maximal time in seconds to wait for the response from Slave station. The station is considered malfunctioning if no valid response is received. This parameter has no meaning for Slave variant of the driver. Do not use long timeouts, especially when there are multiple Slave stations on the bus. In case of a malfunctioning station it is not possible to communicate with other stations for the whole timeout period.
- Reconnect
- – Interval for testing the malfunctioning stations (in seconds).
- Sync. time
- – Synchronization time. The Modbus protocol defines the frame end as silence on the line for a period equal to transmitting 3 characters. Use 0 to respect this timing. All nonzero values define the length of the frame end (in seconds).
[Back to top] [Up] [Next]