Modbus Driver

VOLTTRON’s modbus driver supports the Modbus over TCP/IP protocol only. For Modbus RTU support, see VOLTTRON’s Modbus-TK driver <Modbus-TK-Driver>.

About Modbus protocol

Modbus Driver Configuration

Requirements

The Modbus driver requires the pymodbus package. This package can be installed in an activated environment with:

pip install pymodbus

Alternatively this requirement can be installed using bootstrap.py with the --drivers option:

python3 bootstrap.py --drivers

Driver Configuration

There are three arguments for the driver_config section of the device configuration file:

• device_address - IP Address of the device.

• port - Port the device is listening on. Defaults to 502 which is the standard port for Modbus devices.

• slave_id - Slave ID of the device. Defaults to 0. Use 0 for no slave.

The remaining values are as follows:

Here is an example device configuration file:

{
    "driver_config": {"device_address": "10.1.1.2",
                      "port": 502,
                      "slave_id": 5},
    "driver_type": "modbus",
    "registry_config":"config://registry_configs/hvac.csv",
    "interval": 60,
    "timezone": "UTC",
    "heart_beat_point": "heartbeat"
}

A sample MODBUS configuration file can be found in the VOLTTRON repository in examples/configurations/drivers/modbus.config

Modbus Registry Configuration File

The registry configuration file is a CSV file. Each row configures a point on the device.

The following columns are required for each row:

• Volttron Point Name - The name by which the platform and agents running on the platform will refer to this point. For instance, if the Volttron Point Name is HeatCall1 (and using the example device configuration above) then an agent would use pnnl/isb2/hvac1/HeatCall1 to refer to the point when using the RPC interface of the actuator agent.

• Units - Used for meta data when creating point information on the historian.

• Modbus Register - A string representing how to interpret the data register and how to read it from the device. The string takes two forms:

  • “BOOL” for coils and discrete inputs.

  • A format string for the Python struct module. See the Python3 Struct docs for full documentation. The supplied format string must only represent one value. See the documentation of your device to determine how to interpret the registers. Some Examples:

    • “>f” - A big endian 32-bit floating point number.

    • “<H” - A little endian 16-bit unsigned integer.

    • “>l” - A big endian 32-bit integer.

• Writable - Either TRUE or FALSE. Determines if the point can be written to. Only points labeled TRUE can be written to through the ActuatorAgent.

• Point Address - Modbus address of the point. Cannot include any offset value, it must be the exact value of the address.

• Mixed Endian - (Optional) Either TRUE or FALSE. For mixed endian values. This will reverse the order of the Modbus registers that make up this point before parsing the value or writing it out to the device. Has no effect on bit values.

The following column is optional:

• Default Value - The default value for the point. When the point is reverted by an agent it will change back to this value. If this value is missing it will revert to the last known value not set by an agent.

Any additional columns will be ignored. It is common practice to include a Point Name or Reference Point Name to include the device documentation’s name for the point and Notes and Unit Details for additional information about a point.

The following is an example of a Modbus registry configuration file:

Catalyst 371

Reference Point Name	Volttron Point Name	Units	Units Details	Modbus Register	Writable	Point Address	Default Value	Notes
CO2Sensor	ReturnAirCO2	PPM	0.00-2000.00	>f	FALSE	1001		CO2 Reading 0.00-2000.0 ppm
CO2Stpt	ReturnAirCO2Stpt	PPM	1000.00 (default)	>f	TRUE	1011	1000	Setpoint to enable demand control ventilation
Cool1Spd	CoolSupplyFanSpeed1	%	0.00 to 100.00 (75 default)	>f	TRUE	1005	75	Fan speed on cool 1 call
Cool2Spd	CoolSupplyFanSpeed2	%	0.00 to 100.00 (90 default)	>f	TRUE	1007	90	Fan speed on Cool2 Call
Damper	DamperSignal	%	0.00 - 100.00	>f	FALSE	1023		Output to the economizer damper
DaTemp	DischargeAirTemperature	F	(-)39.99 to 248.00	>f	FALSE	1009		Discharge air reading
ESMEconMin	ESMDamperMinPosition	%	0.00 to 100.00 (5 default)	>f	TRUE	1013	5	Minimum damper position during the energy savings mode
FanPower	SupplyFanPower	kW	0.00 to 100.00	>f	FALSE	1015		Fan power from drive
FanSpeed	SupplyFanSpeed	%	0.00 to 100.00	>f	FALSE	1003		Fan speed from drive
HeatCall1	HeatCall1	On / Off	on/off	BOOL	FALSE	1113		Status indicator of heating stage 1 need
HeartBeat	heartbeat	On / Off	on/off	BOOL	FALSE	1114		Status indicator of heating stage 2 need

A sample Modbus registry file can be found here or in the VOLTTRON repository in examples/configurations/drivers/catalyst371.csv