PIERRE Partner - Generic Modbus

Select the Controller.

For Modbus RTU configuration, select the Configurable I/O tab.

Tap Add and select Modbus RTU.

Required fields: 

• Name – Enter a name for the Modbus device.

• Role – Select the appropriate Role.

• TX – Select the TX pin assigned to the controller.

• RX – Select the RX pin assigned to the controller.

• Baud – Select the Modbus communication baud rate. Available values range from 2400 to 115200 baud.

• Parity – Select the parity setting used by the Modbus device.

• Stop Bits – Select the number of stop bits used by the Modbus device.

Select the Controller.

For Modbus TCP configuration, select the Services tab.

Tap Add and select Modbus TCP.

Required fields: 

• Name – Enter a name for the Modbus device.

• Role – Select the appropriate Role.

• Host – Enter the IP address or hostname of the Modbus TCP device.

• Port – Enter the TCP port used by the Modbus device.

• RTU over TCP – Enable this option for devices that use Modbus RTU communication over a TCP socket.

After creating a Modbus TCP or Modbus RTU device on the controller, you can add a Modbus Generic I/O from the Devices tab.

The Modbus Generic I/O allows you to configure the required Modbus registers and use them within the PIERRE system.

Enter a name for the Generic Modbus device.

The Address field specifies the Modbus Unit Identifier. Refer to the documentation of the target device for the correct address.

Click Add new I/O type to add a predefined type for a supported Modbus device.

Select the Modbus Generic I/O type for a custom Modbus device.

Here you can find all supported device types, including Fan Coil, Energy, Temperature Sensor, Volume, and more.

After creating a Modbus Generic I/O, tap Add new I/O type to select a predefined device type that can be integrated with PIERRE.

Select the required I/O type, such as a Temperature Sensor. Depending on the selected I/O type, you may need to add one or more Modbus register fields.

Use the table above to select the correct register fields for each Modbus Generic I/O type.

• Address – Enter the address of the Modbus register or coil.

• Type – Select the Modbus register type:

  • Coil – Used for coil-based data.

  • Discrete Input – Used for discrete input data.

  • Input Register – Used for read-only input registers.

  • Holding – Uses FC03 – Read Holding Registers for reading and FC06 – Write Single Register for writing.

  • Holdings – Uses FC03 – Read Holding Registers for reading and FC16 (0x10) – Write Multiple Registers for writing.

• Data Type – Defines how the data is interpreted. Select the data type according to the format used by the Modbus device:

  • UInt16 – 16-bit unsigned integer.

  • UInt32 – 32-bit unsigned integer.

  • UInt64 – 64-bit unsigned integer.

  • Int16 – 16-bit signed integer.

  • Int32 – 32-bit signed integer.

  • Int64 – 64-bit signed integer.

  • Float – Floating-point value, typically used for measurements with decimal values, such as temperature or energy.

• Read Function – Applies a transformation to the value read from the Modbus device. This can be used when the raw Modbus value needs to be converted into the value required by PIERRE:

  • Divide – Divides the read value by a specified value.

  • Multiply – Multiplies the read value by a specified value.

  • Swap – Changes the byte or word order of the received value.

  • Mask – Extracts specific bits from the received value.

  • Add – Adds a specified value to the received value.

  • Subtract – Subtracts a specified value from the received value.

  • Bit Shift – Shifts the bits of the received value left or right.

• Write Function – Applies a transformation to the value before it is written to the Modbus device:

  • Divide – Divides the value before writing it to the device.

  • Multiply – Multiplies the value before writing it to the device.

  • Swap – Changes the byte or word order before writing the value.

  • Mask – Applies a bit mask to the value before writing it.

  • Add – Adds a specified value before writing the value.

  • Subtract – Subtracts a specified value before writing the value.

  • Bit Shift – Shifts the bits of the value left or right before writing it.

• Poll Interval – Defines how frequently PIERRE reads the value from the Modbus device.

• Access Control – Defines how the register can be accessed:

  • Read & Write – The register can be both read from and written to.

  • Read – The register can only be read from the device.

  • Write – The register can only be written to the device.

• Loopback – Enables or disables loopback for the register field.

Modbus registers must be addressed according to the addressing scheme specified by the manufacturer in order to access them.

Note that the register addresses defined in the manufacturer's documentation are sometimes different from the protocol addresses that must be used for Modbus communication. For example, with the Midea device described above, the manufacturer specifies the protocol address for input registers as [Register Address] − 30001 and for holding registers as [Register Address] − 40001. However, based on experimental testing, holding register addresses only require 40000 to be subtracted.

This means that the register address for the Target field is 2 for reading the parameter and 4 for modifying it.

This refers to the register type and the Modbus function code used to access the register.

In most cases, manufacturers use Holding Registers for both reading and writing, or Input Registers for reading data and Holding Registers for writing data.

In the example above, the Target field used for reading is configured as Input, while the Target field used for writing is configured as Holdings.

A single Modbus register contains two bytes (16 bits) of data. In most cases, when controlling a device such as a fan coil, a field is handled as a single Modbus register containing an unsigned integer value.

However, some devices that provide precise physical measurements, such as smart electricity meters or heat meters, may use multiple consecutive Modbus registers to store larger values.

For these cases, refer to the datasheet of the target device and select the appropriate Data Type.

Modbus device manufacturers specify how the data in each register should be handled. In the PIERRE application, you can use the Read Function and Write Function options to specify how the data should be processed.

In the example used to illustrate the configuration process, the Input Register for the Target field specifies that the stored temperature value is multiplied by 10. This means that after reading the value, we need to divide it by 10 to obtain the actual temperature.

Therefore, we need to add Read Function → Divide with Data = 10.

For other values, the Swap function can be used for fields such as Heating Season and Mode.

For example, if a thermostat specifies that the value 0 corresponds to OFF and the value 1 corresponds to ON, but PIERRE requires the value 2 for AUTO, the value can be remapped using the Swap function.

Open the Read Functions menu and tap Add data pair.

Tap Add data pair to create a mapping between Modbus values and PIERRE values.

For example:

• Modbus Value: 1

• PIERRE Value: 2

Each pair defines how an incoming Modbus value is translated into the corresponding PIERRE value.

You can add multiple pairs if the device supports several operating modes.

After defining all pairs, the function will appear in the list, for example, as “Swap 1 → 2”.

Tap Done to save the configuration.

From now on, whenever PIERRE reads the Modbus register, the system will automatically apply the defined mapping.

Sometimes a register contains two bytes, or 16 bits, of data, but only a few of those bits are relevant to us. For example, a register may use bit 0 to indicate the Active state.

In this case, the Mask function can be used to extract the relevant bit from the register value.

Set Read function

Similar to the scenario above, you may have a parameter such as Intensity with intensity levels ranging from 0 to 3, while the corresponding data is stored in bits 2 and 3 of the register.

In this case, the values need to be shifted left by two bits, resulting in the following mapping:

• 0 → 0

• 1 → 4

• 2 → 8

• 3 → 12

This could be achieved using a Swap function, but using a Bit Shift is more efficient. Set the Bit Shift function to shift the value left by 2 bits.

Poll Interval:

The PIERRE BMS periodically reads the data specified from a Modbus device. This configuration parameter determines how frequently the data is read for each field.

By default, the Value field is set to 30 seconds, as it is assumed to contain slowly changing physical values. All other fields are set to 2 seconds, as these values may change abruptly due to user interaction.

Only modify the default values when absolutely necessary, as changing them may affect the responsiveness of the entire system.

Access Control:

Depending on whether a parameter is monitored and controlled using the same register or separate read and write registers, the Access Control should be set to Read & Write, Read, or Write, respectively.

Loopback:

This feature allows you to integrate Daikin HVAC systems, as the manufacturer requires a specific control flow for these devices.

In detail, in these systems, the Input Register value can be modified by both the BMS and the wall thermostats. These registers can also be used to read the corresponding PIERRE field values. The Daikin DIII-Modbus Gateway requires any change made by a tenant using a wall thermostat to be synchronized to the corresponding Holding Register by the BMS. Otherwise, the system will not operate correctly.

In a nutshell, when working with Daikin HVAC systems that use separate registers for parameter monitoring and control, the Loopback option MUST BE enabled for the read register of the Field Register pair. Otherwise, leave it disabled by default.