Modbus TCP/IP configuration
Modbus TCP/IP server menu and configuration settings
To enable Modbus TCP/IP feature on the Aranet base station, in the WebGUI navigate to the main menu sidebar item shown in Fig. 1. Please note that use Modbus TCP/IP server feature requires appropriate licence file to be uploaded on the base station.
Figure 1: WebGUI main sidebar menu.
Figure 2: TCP/IP configuration menu
The following items are shown in the Modbus TCP/IP configuration panel as indicated in Fig. 2:
Status of Modbus TCP/IP server process
Switch to enable or disable server process.
Field to specify TCP port number (default is 502).
Set Modbus TCP/IP server Unit ID (a.k.a. Device ID). This must be the same as one set in TCP/IP Client side. In some Client (Master) applications, this setting may be referred to as ”Slave ID”. Client requests with incorrect Unit ID on the Modbus TCP/IP server side will be ignored (communication timeout);
Reset auto-generated address-to-measurements mapping configuration file. WARNING: all addresses used will be reset and may differ from those assigned in previous default mapping file. This request does not affect addressing defined by “Custom layout file”.
Download auto-generated address-to-measurements mapping configuration file.
Switch to enable or disable custom mapping configuration file usage. (This feature allows to upload a userspecified address-to-measurements configuration file.)
Button to save configuration changes.
Button to revert the previous configuration without saving changes.
Process status description
SUCCESS_NO_ERR
No error. Modbus TCP/IP service functions correctly
MODBUS_DISABLED_BY_USER
Service is disabled by the user. Service is not working
MODBUS_DISABLED_BY_LICENCE
An appropriate license is not available to run this service. Service is not working.
WARN_ADDR_COLLISION
Warning state. Registry address overlaps with other address (more info in “details”). Modbus server continues to accept incoming requests and sends responses except for the registers with colliding addresses.
WARN_OFFSET_OR_ADDRESS_OUT_OF_RANGE
Warning state. One or more used offset values or resulting registry addresses (sum of all three offsets per measurement) are out of the expected range (0–65535). Modbus server continues to accept incoming requests and sends responses except for the registers with invalid offset values or resulting registry addresses (more info in “details”).
ERR_CONTEXT_FAILED
Error occurred. Process failed to allocate memory for the Modbus TCP/IP server instance (not enough free memory).
ERR_MAP_ALLOC_FAILED
Error occurred. Modbus address mapping instance allocation failed (not enough free memory).
ERR_CONTEXT_NULL
Error occurred. Error on opening Modbus TCP/IP server socket.
ERR_LISTEN_FAILED
Error occurred. Failed to listen for incoming Modbus TCP/IP connections (port already in use).
ERR_CONFIG_JSON_FAILED
Error occurred. Failed to load mapping configuration JSON file.
SERV_SETTINGS_ERR_CONFIG_LOAD
Error occurred. Failed to load settings configuration file (in order to load Modbus service settings).
SERV_SETTINGS_ERR_JSON_EMPTY
Error occurred. The settings configuration file has an invalid JSON structure.
SERV_SETTINGS_ERR_WRONG_PORT
Error occurred. Incorrect port number in the service configuration.
ERR_OFFSET_MISSING
Error occurred. Offset field is missing or type is incorrect in mapping configuration (more info in “details”).
Address-to-measurements mapping configuration file
Modbus object types
Modbus protocol has four object types (usage depends on desired functionality and data type). It is expected that in the configuration file there are all four of these objects defined.
Modbus protocol has four object types (usage depends on desired functionality and data type). It is expected that in the configuration file there are all four of these objects defined.
coils
1
1
Yes
Yes
discreteInputs
1
1
Yes
No
inputRegisters
1
16
Yes
No
holdingRegisters
16
Yes
Yes
Each type has its own address range. Each range has an offset defined by the field named offset. The address value is limited to two bytes (0–65535). There is no binding between each object type and specific address range, e.g., coils can have a range 0–9999, discrete inputs 10000–19999, input registers 20000–29999, holding registers 30000–39999, or any other configuration.
Current implementation supports discreteInputs and inputRegisters object types only. Addresses can be in the range 0–65535. All other types can be defined in the configuration file, but they will be ignored. It refers also to function codes. Only function codes 2 (read discreteInputs) and 4 (read inputRegisters) are supported.
Example minimal JSON showing an offset:
Discrete input type returns sensors' “packets lost” (RSSI alarm) state: 0 (alarm inactive) or 1 (alarm active, sensor is lost). Implementation is available starting from firmware version 3.2.4. Starting from version 4.8.x, measurement threshold alarm states can also be read from discrete input registers.
Object type to sensor mapping
Each Modbus object type can have a set of sensors as nested JSON objects. For each sensor object, there is expected to have its own address offset within its parent Modbus object type address range. Here is an example with sensors mapped to Modbus data type having offsets defined:
Numbers “1056849” and “4196581” are internal sensor identificators. Sensors HEX identificator is mentioned in the comment of the auto-generated address-to-measurements mapping configuration file (see “Confguration controls”, Pt. 4) in the same line next to the sensor identificator.
Address-to-sensor-to-measurement mapping
Each measurement has a field named offset which is mandatory for each object and must have a unique value between that sensor’s other measurement offset values (same rule applies also to sensors – unique offset value between sensors). Sum of all three offset values determines initial address for register. Example:
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