Modbus Driver Configuration

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


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.

Here is an example device configuration file:

    "driver_config": {"device_address": "",
                      "port": 502,
                      "slave_id": 5},
    "driver_type": "modbus",
    "interval": 60,
    "timezone": "UTC",
    "heart_beat_point": "heartbeat"

A sample MODBUS configuration file can be found in the VOLTTRON repository in examples/configurations/drivers/modbus1.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 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 confugration 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