Item Syntax neutral

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Modern PLCs don't need an item syntax. All symbols are available on the controller. They will be read online. This applies to all Rockwell ControlLogic and CompactLogix PLCs, all Siemens S7 1500 and 1200 models, and BACnet devices.

Some subsystems as MQTT do not know variables with defined data types. For these the neutral item syntax is offered also.

For MQTT the usage of this item syntax need to be configured in the connection parameters.

A tag is fully defined with the tag name, the data type is defined by the PLC. Normally, nothing needs to be added.

However, there are some exceptions:

•	Addressing a single element of an array: the zero-based index is specified in square brackets after the item name.

<Tagname>[<index>]

If you need offline symbols, you can add them. This may be required:

•	to have symbols without a controller online,

•	to rename symbols

•	for simulation connections.

The "item syntax" is the real symbol name in the controller.

Because no data type is available without online access to the PLC an optional name extension exists for specifying the type.

The rule is:

<Symbolname>{{<Datatype>,<Endian>}}

or for arrays:

<Symbolname>{{<Datatype>,<Arraylength>,<Endian>}}

The following data types are allowed (the spaces are important):

Bool

Int 8

Int 16

Int 32

Int 64

Uint 8

Uint 16

Uint 32

Uint 64

Float

Double

Timestamp

String

These is possible for endian:

LittleEndian, some times known as INTEL format

BigEndian, known as Motorola format

If non endian is given the format of the locally working cpu is used.

The symbol name (without the {{ }} name extension) must be present in the controller (except for simulation connections).