Modbus RTU

The element allows to get data from MODBUS RTU device and to write data to MODBUS RTU device.

Requests for management:

addvirtual - add a virtual sensor. Extra options are:

• k - user session ID;
• id - the identifier of the element; if the identifier is absent, a new element is created; otherwise the existing one is modified;
• name - the name of the element, the length is not more than 63 characters;
• virtual_type - type of virtual sensor:
  • modbus rtu - for reading Modbus data;
  • modbus rtu write - for writing Modbus data.

Options for reading Modbus data only (analog virtual sensor):

• vmax - maximum value for the measuring range;
• vmin - minimum value for the measuring range;
• low_alarm - threshold level for notification;
• low_warning - threshold level for notification;
• high_warning - threshold level for notification;
• high_alarm - threshold level for notification;
• hyst_type - the type of algorithm used to calculate the hysteresis:
  • disable - the hysteresis is disabled;
  • value - hysteresis by the value measured by the sensor value;
  • time - hysteresis using time (used by default).
• hyst_value - the value of the deviation of the sensor value when calculating the hysteresis by value, the value with a floating point (minimum 0, maximum 10,000, default 0.3);
• hyst_low_alarm - the time in seconds, during which the sensor should keep its value in this range, for transition of the sensor to this state (minimum 0, maximum 1000, default 1);
• hyst_low_warning - same as previous (default 1);
• hyst_normal - same as previous (default is 0);
• hyst_high_warning - same as previous (default 1);
• hyst_high_alarm - same as previous (default 1).
• expr - expression for calculating the output value, by default "x";
• um - unit of measurement of this element;
• utype - custom type, defines the sensor icon: current, factor, frequency, humidity, power, temperature, vibration, voltage;

Options for Modbus protocol (reading only):

• mb_addr - slave address of device on bus, decimal (1-255);
• mb_reg - register index for modbus function, hexademal string;
• mb_func - function code for modbus:
  • Read Coil Status (0x01);

  • Read Input Status (0x02);

  • Read Holding Register (0x03);

  • Read Input Register (0x04).

• mb_type - data type:
  

  1. 16 bits signed int;

  2. 16 bits unsigned int;

  3. 32 bits signed int;

  4. 32 bits unsigned int;

  5. 32 bits IEEE 754 floating point.

• mb_order - data ordering:
  

  1. low byte first, low word first;

  2. low byte first, high word first;

  3. high byte first, low word first;

  4. high byte first, high word first.

• mb_period - the polling period, seconds.

Options for Modbus protocol (writing only):

• mb_addr - slave address of device on bus, decimal (1-255);
• mb_reg - register index for modbus function, hexademal string;
• mb_func - function code for modbus:
  • Write Single Coil (0x05);

  • Write Single Register (0x06).

• mb_wrval - writing value, integer.

If the new element is successfully created, the response is:

When creating a new sensor (id is not specified), some parameters are mandatory. For reading: name, virtual_type, vmax, vmin, mb_addr, mb_reg, mb_func, mb_type, mb_order, mb_period. For writing: name, virtual_type, mb_addr, mb_reg, mb_func, mb_wrval. The rest of the query parameters are optional, and if not set, they will be set to the default values.

When editing an element, you can change individual fields.

delvirtual - remove the virtual sensor. Extra options:

• k - user session ID;
• id - ID of the element.

getelement - read the element. Extra options are:

• k - the user session ID;
• id - the ID of the item.

Information about the element looks like:

Modbus RTU configuration

Requests for management:

setmodbus - communication settings of Modbus RTU. Extra options are:

• k - user session ID;
• enable - enable Modbus interface and Modbus RTU virtual sensors (0 by default);
• baud - baud rate of the communication (1200, 2400, 4800, 9600, 19200, 57600, 115200);
• parity - parity check of the communication (none, even, odd);
• stopbit - number of stop bits (1 or 2);

getmodbus - read the communication configuration of Modbus.

• k - the user session ID.

Information about the communication looks like:

If no hardware support:

Modbus RTU communication test

Requests for management:

testvirtual - communication test of Modbus RTU. Extra options are:

• k - user session ID;
• virtual_type - type of virtual sensor:
  • modbus rtu - for reading Modbus data;
  • modbus rtu write - for writing Modbus data.
• mb_addr - slave address of device on bus, decimal (1-255);
• mb_reg - register index for modbus function, hexademal string;
• mb_func - function code for modbus:
  • Read Coil Status (0x01);

  • Read Input Status (0x02);

  • Read Holding Register (0x03);

  • Read Input Register (0x04);

  • Write Single Coil (0x05);

  • Write Single Register (0x06).

• mb_type - data type (for reading only):
  

  1. 16 bits signed int;

  2. 16 bits unsigned int;

  3. 32 bits signed int;

  4. 32 bits unsigned int;

  5. 32 bits IEEE 754 floating point.

• mb_order - data ordering (for reading only):
  

  1. low byte first, low word first;

  2. low byte first, high word first;

  3. high byte first, low word first;

  4. high byte first, high word first.

• mb_wrval - writing value, integer (for writing only).

Information about the reading test looks like:

If an error occurs, example:

If no error occurs, the writing test looks like:

If Modbus is disabled or not supported: