Modbus Connection

ModbusConnection

class eta_nexus.connections.ModbusConnection(url: str, usr: str | None = None, pwd: str | None = None, *, nodes: Nodes[ModbusNode] | None = None)[source]

The Modbus Connection class allows reading and writing from and to Modbus servers and clients. Additionally, it implements a subscription service, which reads continuously in a specified interval.

Parameters:

url – URL of the Modbus Server.
usr – No login supported, only here to satisfy the interface
pwd – No login supported, only here to satisfy the interface
nodes – List of nodes to use for all operations.

logger: Logger = <Logger eta_nexus.connections.modbus_connection (WARNING)>

connection: ModbusClient

read(nodes: ModbusNode | Nodes[ModbusNode] | None = None) → pd.DataFrame[source]

Read some manually selected nodes from Modbus server.

Parameters:: nodes – Single node or list/set of nodes to read from.
Returns:: Dictionary containing current values of the Modbus variables.

write(values: Mapping[ModbusNode, Primitive]) → None[source]

Write some manually selected values on Modbus capable controller.

Parameters:: values – Dictionary of nodes and data to write {node: value}.

subscribe(handler: SubscriptionHandler, nodes: ModbusNode | Nodes[ModbusNode] | None = None, interval: TimeStep = 1) → None[source]

Subscribe to nodes and call handler when new data is available. Basic architecture of the subscription is the client- server communication. This function works asynchronously.

Parameters:

nodes – Single node or list/set of nodes to subscribe to.
handler – SubscriptionHandler object with a push method that accepts node, value pairs.
interval – Interval for receiving new data. It is interpreted as seconds when given as an integer.

close_sub() → None[source]: Close the subscription.

url_parsed: ParseResult: URL of the server to connect to

usr: str | None: Username for login to server

pwd: str | None: Password for login to server

exc: BaseException | None

ModbusNode

class eta_nexus.nodes.ModbusNode(name: str, url: str, protocol: str, *args: Any, **kwargs: Any)[source]

Node for the Modbus protocol.

mb_slave: int | None: Modbus Slave ID

mb_register: str: Modbus Register name. One of input, discrete_input, coils and holding. Note that only coils and holding can be written to.

mb_channel: int: Modbus Channel (Address of the value)

mb_bit_length: int: Length of the value in bits (default 32). This determines, how much data is read from the server. The value must be a multiple of 16.

mb_byteorder: str: Byteorder of values returned by modbus

mb_wordorder: str: Wordorder of values returned by modbus

decode_modbus_value(value: Sequence[int]) → Any[source]

Decode incoming modbus values.

Strings are always decoded as utf-8 values. If you do not want this behaviour, specify ‘bytes’ as the data type for the Node.

Parameters:: value – Current value to be decoded
Returns:: Decoded value as the Node’s data type.

encode_bits(value: Primitive) → list[int][source]

Encode python data type to modbus value. This means an array of bytes to send to a modbus server.

Parameters:: value – Current value to be decoded into float.
Returns:: Decoded value as a python type.

connection_identifier() → str: Unique identifier for the connection that is associated with the node (i.e. would be created by Connection.from_node())

name: str: Name for the node.

url: str: URL of the connection.

url_parsed: ParseResult: Parse result object of the URL (in case more post-processing is required).

usr: str | None: Username for login to the connection (default: None).

pwd: str | None: Password for login to the connection (default: None).

interval: str | None: Interval

dtype: Callable | None: Data type of the node (for value conversion). Note that strings will be interpreted as utf-8 encoded. If you do not want this behaviour, use ‘bytes’.