Copy settings from Simply MODBUS RTU Master to our Modbus Data Logger

1. Create a new configuration from the main window using the "Green Plus" button. (fig. 2). This example shows the connection settings for MODBUS RTU. If your device uses MODBUS TCP, look here. Copy all communication parameters from Simply MODBUS:

• COM port → COM ports.
• Baud → Baud rate.
• Data bits → Data bits.
• Stop bits → Stop bits.
• Parity → Parity.
• Spy mode - disable this option.
• RS485 mode - enable this option, if you connected your MODBUS are on an RS-485 bus, and you use RS485-USB or RS485-RS232 converter.
• Other options - leave the default value as shown below.

Fig. 2: Configuring RS232 MODBUS RTU connection.

2. Activate the "MODBUS RTU" plugin in the settings in both fields "Data query module" and "Parser module" (fig. 3). Please (do not confuse it with "MODBUS RTU [Passive]" or "MODBUS RTU [Slave]" because they realize other functionality. We configure the MODBUS master station. Note: If your settings "Register size" is "32 bit registers", you should select the "MODBUS RTU [Enron]" in both fields.

Fig. 3: Activating the MODBUS RTU plugin.

3. In the MODBUS RTU plugin settings, click the "Action → Add new request" button to add a new query request (fig. 4). Copy basic request settings from Simply MODBUS:

• Slave ID → Device address.
• Function code → Function.
• The result of the expression (First register - Minus offset) → First register - Value.
• Number of registers → Registers to read.
• The result of the expression (Response time * 2 * 1000) → Request timeout (ms).
• Polling - configure it as you want.

Fig. 4: Basic MODBUS query settings.

4. Add the necessary number of response items by clicking the "Action → Add response item" button:

• Name - any name of this value.
• Offset - it is the byte offset in response data without a device address, function code and data size. Set this value to "-1", and the program will calculate an offset automatically.
• Count - the number of sequential values with the identical data type and name.
• Append counter - it is used when "Count" is greater than 1.
• Data type - copy the type from the first column with response data items.
• Unsigned - enable this option if a data type in Simply MODBUS is an unsigned decimal (UINT) and disable in another case (INT).
• Little-endian - it has an inversed state of the "High byte first" option in Simply MODBUS.
• Swapped - it is the same as "High word first".

Note: The figure below is an example. It does not match response items on fig. 1. The full correct list of response items will look like:

1. Name: VALUE1, Offset: -1, Count: 1, Data type: Decimal 16 bit, Unsigned: Off, Little-endian: Off.
2. Name: VALUE2, Offset: -1, Count: 1, Data type: Float, Unsigned: Off, Little-endian: Off, Swapped: On.
3. Name: VALUE3, Offset: -1, Count: 1, Data type: Decimal 32 bit, Unsigned: Off, Little-endian: Off, Swapped: On.
4. Name: VALUE4, Offset: -1, Count: 1, Data type: Decimal 32 bit, Unsigned: On, Little-endian: Off, Swapped: On.

Fig. 5: MODBUS response items.

MODBUS RTU allows you to connect up to 254 devices on one RS-485 bus. You may specify several addresses like 1,2,3,4,5 in the "Device address" field (fig. 4).

Yes, of course. The settings are almost identical. You should configure the TCP connection settings and select other parser type (MODBUS TCP instead of MODBUS RTU) (fig. 3).