Modbus Controller

The modbus_controller component creates a RS485 connection to either:

  • control a Modbus server (slave) device, letting your ESPHome node to act as a Modbus client (master). You can access the coils, inputs, holding, read registers from your devices as sensors, switches, selects, numbers or various other ESPHome components and present them to your favorite Home Automation system. You can even write them as binary or float ouptputs from ESPHome.

  • let your ESPHome node act as a Modbus server, allowing a ModBUS client to read data (like sensor values) from your ESPHome node.

To choose the role, set the role attribute of the Modbus Component upon which this modbus_controller component relies. client is the default.

../_images/modbus.png

Hardware setup

You need an RS485 transceiver module:

../_images/rs485.jpg

See How is this RS485 module working? on stackexchange for more details.

The transceiver connects to the UART of the MCU. For ESP32, pin 16 to TXD and pin 17 to RXD are the default ones but any other pins can be used as well. 3.3V to VCC and naturally GND to GND.

On the bus side, you need 120 Ohm termination resistors at the ends of the bus cable as per Modbus standard. Some transceivers have this already soldered onboard, while some slave devices may have them available via a jumper or a DIP switch.

Note

If you are using an ESP8266, serial logging may cause problems reading from UART. For best results, hardware serial is recommended. Software serial may not be able to read all received data if other components spend a lot of time in the loop().

For hardware serial only a limited set of pins can be used. Either tx_pin: GPIO1 and rx_pin: GPIO3 or tx_pin: GPIO15 and rx_pin: GPIO13.

The disadvantage of using the hardware UART is that you can’t use serial logging because the serial logs would be sent to the Modbus device(s) instead, causing errors.

Serial logging can be disabled by setting baud_rate: 0.

See Logger Component for more details

logger:
    level: <level>
    baud_rate: 0

Configuration variables:

  • modbus_id (Optional, ID): Manually specify the ID of the modbus hub.

  • address (Required, ID): The Modbus address of the slave device

  • command_throttle (Optional, Time): minimum time in between 2 requests to the device. Default is 0ms. Some Modbus slave devices limit the rate of requests from the master, so this allows the interval between requests to be altered.

  • update_interval (Optional, Time): The interval that the sensors should be checked. Defaults to 60 seconds.

  • offline_skip_updates (Optional, integer): When a slave doesn’t respond to a command, it is marked as offline, you can specify how many updates will be skipped while it is offline. If using a bus with multiple slaves, this avoids waiting for timeouts allowing to read other slaves in the same bus. When the slave responds to a command, it’ll be marked online again.

  • server_registers (Optional): A list of registers that are responded to when acting as a server. - start_address (Required, integer): start address of the first register in a range - value_type (Optional): datatype of the mod_bus register data. The default data type for ModBUS is a 16 bit integer in big endian format (MSB first)

    • U_WORD: unsigned 16 bit integer from 1 register = 16bit

    • S_WORD: signed 16 bit integer from 1 register = 16bit

    • U_DWORD: unsigned 32 bit integer from 2 registers = 32bit

    • S_DWORD: signed 32 bit integer from 2 registers = 32bit

    • U_DWORD_R: unsigned 32 bit integer from 2 registers low word first

    • S_DWORD_R: signed 32 bit integer from 2 registers low word first

    • U_QWORD: unsigned 64 bit integer from 4 registers = 64bit

    • S_QWORD: signed 64 bit integer from 4 registers = 64bit

    • U_QWORD_R: unsigned 64 bit integer from 4 registers low word first

    • S_QWORD_R: signed 64 bit integer from 4 registers low word first

    • FP32: 32 bit IEEE 754 floating point from 2 registers

    • FP32_R: 32 bit IEEE 754 floating point - same as FP32 but low word first

    Defaults to U_WORD.

    • lambda (Required, lambda): Lambda that returns the value of this register.

Example Client

The following code creates a modbus_controller hub talking to a ModBUS device at address 1 with 115200 bps

ModBUS sensors can be directly defined (inline) under the modbus_controller hub or as standalone components Technically there is no difference between the “inline” and the standard definitions approach.

# Example configuration entry
uart:
  ...

modbus:
  flow_control_pin: GPIOXX
  id: modbus1

modbus_controller:
- id: modbus_device
  address: 0x1   ## address of the Modbus slave device on the bus
  modbus_id: modbus1
  setup_priority: -10

sensor:
- platform: modbus_controller
  modbus_controller_id: modbus_device
  name: "Battery Capacity"
  register_type: holding
  address: 0x9001    ## address of the register inside the Modbus slave device
  unit_of_measurement: "AH"
  value_type: U_WORD

switch:
- platform: modbus_controller
  modbus_controller_id: modbus_device
  name: "Reset to Factory Default"
  register_type: coil
  address: 0x15
  bitmask: 1

text_sensor:
- name: "rtc_clock"
  platform: modbus_controller
  modbus_controller_id: modbus_device
  id: rtc_clock
  internal: true
  register_type: holding
  address: 0x9013
  register_count: 3
  raw_encode: HEXBYTES
  response_size: 6

The configuration example above creates a modbus_controller hub talking to a Modbus device at address 1 with a baudrate of 115200 bps, implementing a sensor, a switch and a text sensor.

Example Server

The following code allows a ModBUS client to read a sensor value from your ESPHome node, that the node itself read from a ModBUS server.

uart:
  - id: uart_modbus_client
    tx_pin: 32
    rx_pin: 34
  - id: uart_modbus_server
    tx_pin: 25
    rx_pin: 35

modbus:
  - uart_id: uart_modbus_client
    id: modbus_client
  - uart_id: uart_modbus_server
    id: modbus_server
    role: server

modbus_controller:
  - id: modbus_evse
    modbus_id: modbus_client
    address: 0x2
    update_interval: 5s
  - modbus_id: modbus_server
    address: 0x4
    server_registers:
      - start_address: 0x0002
        value_type: S_DWORD_R
        lambda: |-
          return id(evse_voltage_l1).state;

sensor:
  - platform: modbus_controller
    id: evse_voltage_l1
    modbus_controller_id: modbus_evse
    name: "EVSE voltage L1"
    register_type: holding
    address: 0x0000
    device_class: voltage
    value_type: S_DWORD_R
    accuracy_decimals: 1
    unit_of_measurement: V
    filters:
      - multiply: 0.1

Check out the various Modbus components available at the bottom of the document in the See Also section. They can be directly defined (inline) under the modbus_controller hub or as standalone components. Technically there is no difference between the inline and the standard definitions approach.

Below you find a few general tips about using Modbus in more advanced scenarios. Applicable component functionalities have links pointing here:

Bitmasks

Some devices use decimal values in read registers to show multiple binary states occupying only one register address. To decode them, you can use bitmasks according to the table below. The decimal value corresponding to a bit is always double of the previous one in the row. Multiple bits can be represented in a single register by making a sum of all the values corresponding to the bits.

Alarm bit

Description

DEC value

HEX value

bit 0

Binary Sensor 0

1

1

bit 1

Binary Sensor 1

2

2

bit 2

Binary Sensor 2

4

4

bit 3

Binary Sensor 3

8

8

bit 4

Binary Sensor 4

16

10

bit 5

Binary Sensor 5

32

20

bit 6

Binary Sensor 6

64

40

bit 7

Binary Sensor 7

128

80

bit 8

Binary Sensor 8

256

100

bit 9

Binary Sensor 9

512

200

bit 10

Binary Sensor 10

1024

400

bit 11

Binary Sensor 11

2048

800

bit 12

Binary Sensor 12

4096

1000

bit 13

Binary Sensor 13

8192

2000

bit 14

Binary Sensor 14

16384

4000

bit 15

Binary Sensor 15

32768

8000

In the example below, register 15, holds several binary values. It stores the decimal value 12288, which is the sum of 4096 + 8192, meaning the corresponding bits 12 and 13 are 1, the other bits are 0.

To gather some of these bits as binary sensors in ESPHome, use bitmask:

binary_sensor:
- platform: modbus_controller
  modbus_controller_id: modbus1
  name: Alarm bit0
  register_type: read
  address: 15
  bitmask: 0x1
- platform: modbus_controller
  modbus_controller_id: modbus1
  name: Alarm bit1
  register_type: read
  address: 15
  bitmask: 0x2
- platform: modbus_controller
  modbus_controller_id: modbus1
  name: Alarm bit10
  register_type: read
  address: 15
  bitmask: 0x400
- platform: modbus_controller
  modbus_controller_id: modbus1
  name: Alarm bit15
  register_type: read
  address: 15
  bitmask: 0x8000

Using custom_command

custom_command can be used to create an arbitrary modbus command. Combined with a lambda any response can be handled. This example re-implements the command to read the registers 0x156 (Total active energy) and 0x158 Total (reactive energy) from a SDM-120. SDM-120 returns the values as floats using 32 bits in 2 registers.

uart:
  id: mod_uart
  ...

modbus:
  send_wait_time: 200ms
  uart_id: mod_uart
  id: mod_bus

modbus_controller:
- id: sdm
  address: 2
  modbus_id: mod_bus
  command_throttle: 100ms
  setup_priority: -10
  update_interval: 30s

sensors:
- platform: modbus_controller
  modbus_controller_id: sdm
  name: "Total active energy"
  id: total_energy
  #    address: 0x156
  #    register_type: "read"
  ## reimplement using custom_command
  # 0x2 : modbus device address
  # 0x4 : modbus function code
  # 0x1 : high byte of modbus register address
  # 0x56: low byte of modbus register address
  # 0x00: high byte of total number of registers requested
  # 0x02: low byte of total number of registers requested
  custom_command: [ 0x2, 0x4, 0x1, 0x56,0x00, 0x02]
  value_type: FP32
  unit_of_measurement: kWh
  accuracy_decimals: 1

- platform: modbus_controller
  modbus_controller_id: sdm
  name: "Total reactive energy"
  #   address: 0x158
  #   register_type: "read"
  custom_command: [0x2, 0x4, 0x1, 0x58, 0x00, 0x02]
  ## the command returns an float value using 4 bytes
  lambda: |-
      ESP_LOGD("Modbus Sensor Lambda","Got new data" );
      union {
        float float_value;
        uint32_t raw;
      } raw_to_float;
      if (data.size() < 4 ) {
        ESP_LOGE("Modbus Sensor Lambda", "invalid data size %d",data.size());
        return NAN;
      }
      raw_to_float.raw =   data[0] << 24 | data[1] << 16 | data[2] << 8 |  data[3];
      ESP_LOGD("Modbus Sensor Lambda", "FP32 = 0x%08X => %f", raw_to_float.raw, raw_to_float.float_value);
      return raw_to_float.float_value;
    unit_of_measurement: kVArh
    accuracy_decimals: 1

Optimizing modbus communications

register_count is an option only required for uncommon response encodings or to optimizie modbus communications.

It describes the number of registers this data point spans, overriding the defaults determined by value_type. If no value for register_count is provided, it is calculated based on the register type. The default size for one register is 16 bits (one word). Some devices are not adhering to this convention and have registers larger than 16 bits. In this case, register_count and response_size must be set. For example, if your Modbus device uses one register for a FP32 value (instead of the default of two), set register_count: 1 and response_size: 4.

register_count can also be used to skip a number of registers in consecutive range.

An example is an SDM meter, with interesting data in register addresses 0, 2, 4 and 6:

- platform: modbus_controller
  name: "Voltage Phase 1"
  address: 0
  register_type: "read"
  value_type: FP32

- platform: modbus_controller
  name: "Voltage Phase 2"
  address: 2
  register_type: "read"
  value_type: FP32

- platform: modbus_controller
  name: "Voltage Phase 3"
  address: 4
  register_type: "read"
  value_type: FP32

- platform: modbus_controller
  name: "Current Phase 1"
  address: 6
  register_type: "read"
  value_type: FP32
  accuracy_decimals: 1

The configuration above will generate one modbus command read multiple registers from 0 to 6.

Maybe you don’t care about the data in register addresses 2 and 4, which are voltage values for Phase 2 and Phase 3 (or you have a SDM-120). Of course, you can delete the sensors your don’t care about, but then you’d have a gap in the addresses. If you remove the registers at address 2 and 4, two commands will be generated – read register 0 and read register 6. To avoid generating multiple commands and thus reduce activity on the bus, register_count can be used to fill the gaps:

- platform: modbus_controller
  name: "Voltage Phase 1"
  address: 0
  unit_of_measurement: "V"
  register_type: "read"
  value_type: FP32
  register_count: 6

- platform: modbus_controller
  name: "Current Phase 1"
  address: 6
  register_type: "read"
  value_type: FP32

Because the option register_count: 6 is used for the first sensor, one command read multiple registers from 0 to 6 will be used but the values in between will be ignored.

Note

Calculation: FP32 is a 32 bit value and uses 2 registers. Therefore, to skip the 2 FP32 registers the size of these 2 registers must be added to the default size for the first register. So we have 2 for address 0, 2 for address 2 and 2 for address 4 thus register_count must be 6.

Protocol decoding example

sensors:
- platform: modbus_controller
  modbus_controller_id: epever
  id: array_rated_voltage
  name: "array_rated_voltage"
  address: 0x3000
  unit_of_measurement: "V"
  register_type: read
  value_type: U_WORD
  accuracy_decimals: 1
  skip_updates: 60
  filters:
    - multiply: 0.01

- platform: modbus_controller
  modbus_controller_id: epever
  id: array_rated_current
  name: "array_rated_current"
  address: 0x3001
  unit_of_measurement: "V"
  register_type: read
  value_type: U_WORD
  accuracy_decimals: 2
  filters:
    - multiply: 0.01

- platform: modbus_controller
  modbus_controller_id: epever
  id: array_rated_power
  name: "array_rated_power"
  address: 0x3002
  unit_of_measurement: "W"
  register_type: read
  value_type: U_DWORD_R
  accuracy_decimals: 1
  filters:
    - multiply: 0.01

- platform: modbus_controller
  modbus_controller_id: epever
  id: battery_rated_voltage
  name: "battery_rated_voltage"
  address: 0x3004
  unit_of_measurement: "V"
  register_type: read
  value_type: U_WORD
  accuracy_decimals: 1
  filters:
    - multiply: 0.01

- platform: modbus_controller
  modbus_controller_id: epever
  id: battery_rated_current
  name: "battery_rated_current"
  address: 0x3005
  unit_of_measurement: "A"
  register_type: read
  value_type: U_WORD
  accuracy_decimals: 1
  filters:
    - multiply: 0.01

- platform: modbus_controller
  modbus_controller_id: epever
  id: battery_rated_power
  name: "battery_rated_power"
  address: 0x3006
  unit_of_measurement: "W"
  register_type: read
  value_type: U_DWORD_R
  accuracy_decimals: 1
  filters:
    - multiply: 0.01

- platform: modbus_controller
  modbus_controller_id: epever id: charging_mode
  name: "charging_mode"
  address: 0x3008
  unit_of_measurement: ""
  register_type: read
  value_type: U_WORD
  accuracy_decimals: 0

To minimize the required transactions all registers with the same base address are read in one request. The response is mapped to the sensor based on register_count and offset in bytes. For example:

Request

data

description

0x1 (01)

device address

0x4 (04)

function code 4 (Read Input Registers)

0x30 (48)

start address high byte

0x0 (00)

start address low byte

0x0 (00)

number of registers to read high byte

0x9 (09)

number of registers to read low byte

0x3f (63)

crc

0xc (12)

crc

Response

offset

data

value (type)

description

H

0x1 (01)

device address

H

0x4 (04)

function code

H

0x12 (18)

byte count

0

0x27 (39)

U_WORD

array_rated_voltage high byte

1

0x10 (16)

0x2710 (100000)

array_rated_voltage low byte

2

0x7 (7)

U_WORD

array_rated_current high byte

3

0xd0 (208)

0x7d0 (2000)

array_rated_current low byte

4

0xcb (203)

U_DWORD_R

array_rated_power high byte of low word

5

0x20 (32)

spans 2 register

array_rated_power low byte of low word

6

0x0 (0)

array_rated_power high byte of high word

7

0x0 (0)

0x0000CB20 (52000)

array_rated_power low byte of high word

8

0x9 (09)

U_WORD

battery_rated_voltage high byte

9

0x60 (96)

0x960 (2400)

battery_rated_voltage low byte

10

0x7 (07)

U_WORD

battery_rated_current high word

11

0xd0 (208)

0x7d0 (2000)

battery_rated_current high word

12

0xcb (203)

U_DWORD_R

battery_rated_power high byte of low word

13

0x20 (32)

spans 2 register

battery_rated_power low byte of low word

14

0x0 (0)

battery_rated_power high byte of high word

15

0x0 (0)

0x0000CB20 (52000)

battery_rated_power low byte of high word

16

0x0 (0)

U_WORD

charging_mode high byte

17

0x2 (02)

0x2 (MPPT)

charging_mode low byte

C

0x2f (47)

crc

C

0x31 (49)

crc

Note

Write support is only implemented for switches and selects; however, the C++ code provides the required API to write to a Modbus device.

These methods can be called from a lambda.

Here is an example how to set config values to for an EPEVER Trace AN controller. The code synchronizes the localtime of MCU to the epever controller The time is set by writing 12 bytes to register 0x9013. Then battery charge settings are sent.

esphome:
  on_boot:
    ## configure controller settings at setup
    ## make sure priority is lower than setup_priority of modbus_controller
    priority: -100
    then:
      - lambda: |-
          // get local time and sync to controller
          time_t now = ::time(nullptr);
          struct tm *time_info = ::localtime(&now);
          int seconds = time_info->tm_sec;
          int minutes = time_info->tm_min;
          int hour = time_info->tm_hour;
          int day = time_info->tm_mday;
          int month = time_info->tm_mon + 1;
          int year = time_info->tm_year % 100;
          esphome::modbus_controller::ModbusController *controller = id(epever);
          // if there is no internet connection localtime returns year 70
          if (year != 70) {
            // create the payload
            std::vector<uint16_t> rtc_data = {uint16_t((minutes << 8) | seconds), uint16_t((day << 8) | hour),
                                              uint16_t((year << 8) | month)};
            // Create a Modbus command item with the time information as the payload
            esphome::modbus_controller::ModbusCommandItem set_rtc_command =
                esphome::modbus_controller::ModbusCommandItem::create_write_multiple_command(controller, 0x9013, 3, rtc_data);
            // Submit the command to the send queue
            epever->queue_command(set_rtc_command);
            ESP_LOGI("ModbusLambda", "EPSOLAR RTC set to %02d:%02d:%02d %02d.%02d.%04d", hour, minutes, seconds, day, month,
                    year + 2000);
          }
          // Battery settings
          // Note: these values are examples only and apply my AGM Battery
          std::vector<uint16_t> battery_settings1 = {
              0,       // 9000 Battery Type 0 =  User
              0x0073,  // 9001 Battery Cap 0x55 == 115AH
              0x012C,  // 9002 Temp compensation -3V /°C/2V
              0x05DC,  // 9003 0x5DC == 1500 Over Voltage Disconnect Voltage 15,0
              0x058C,  // 9004 0x58C == 1480 Charging Limit Voltage 14,8
              0x058C,  // 9005 Over Voltage Reconnect Voltage 14,8
              0x05BF,  // 9006 Equalize Charging Voltage 14,6
              0x05BE,  // 9007 Boost Charging Voltage 14,7
              0x0550,  // 9008 Float Charging Voltage 13,6
              0x0528,   // 9009 Boost Reconnect Charging Voltage 13,2
              0x04C4,  // 900A Low Voltage Reconnect Voltage 12,2
              0x04B0,  // 900B Under Voltage Warning Reconnect Voltage 12,0
              0x04BA,  // 900c Under Volt. Warning Volt 12,1
              0x04BA,  // 900d Low Volt. Disconnect Volt. 11.8
              0x04BA   // 900E Discharging Limit Voltage 11.8
          };

          // Boost and equalization periods
          std::vector<uint16_t> battery_settings2 = {
              0x0000,  // 906B Equalize Duration (min.) 0
              0x0075   // 906C Boost Duration (aka absorb) 117 mins
          };
          esphome::modbus_controller::ModbusCommandItem set_battery1_command =
              esphome::modbus_controller::ModbusCommandItem::create_write_multiple_command(controller, 0x9000, battery_settings1.size() ,
                                                                                          battery_settings1);

          esphome::modbus_controller::ModbusCommandItem set_battery2_command =
              esphome::modbus_controller::ModbusCommandItem::create_write_multiple_command(controller, 0x906B, battery_settings3.size(),
                                                                                          battery_settings2);
          delay(200) ;
          controller->queue_command(set_battery1_command);
          delay(200) ;
          controller->queue_command(set_battery2_command);
          ESP_LOGI("ModbusLambda", "EPSOLAR Battery set");

uart:
  id: mod_bus
  tx_pin: GPIOXX
  rx_pin: GPIOXX
  baud_rate: 115200
  stop_bits: 1

modbus:
  #flow_control_pin: GPIOXX
  send_wait_time: 200ms
  id: mod_bus_epever

modbus_controller:
  - id: epever
    ## the Modbus device addr
    address: 0x1
    modbus_id: mod_bus_epever
    command_throttle: 0ms
    setup_priority: -10
    update_interval: ${updates}

sensor:
  - platform: modbus_controller
    modbus_controller_id: epever
    id: array_rated_voltage
    name: "array_rated_voltage"
    address: 0x3000
    unit_of_measurement: "V"
    register_type: read
    value_type: U_WORD
    accuracy_decimals: 1
    filters:
      - multiply: 0.01

  - platform: modbus_controller
    modbus_controller_id: epever
    id: array_rated_current
    name: "array_rated_current"
    address: 0x3001
    unit_of_measurement: "A"
    register_type: read
    value_type: U_WORD
    accuracy_decimals: 2
    filters:
      - multiply: 0.01

  - platform: modbus_controller
    modbus_controller_id: epever
    id: array_rated_power
    name: "array_rated_power"
    address: 0x3002
    unit_of_measurement: "W"
    register_type: read
    value_type: U_DWORD_R
    accuracy_decimals: 1
    filters:
      - multiply: 0.01

See Also