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Tags are configured using the Device and Item properties and the N2 and N4 parameters.

•Device: Indicates the address of a device as defined in the ABS.ini file, followed by a colon (:), such as 1:. The Modbus address is fixed in 0 (zero)

•N2: Indicates the type of a Tag. Possible values are described on the next table

Possible values for the N2 parameter

 

•N4: Used only for the Event Reading Block Tag, with the N2 parameter equal to 100, informing the type of management of a Logger. Possible values are 0: Does not save the pointer from the last reading when stopping this Driver, 1: Saves the pointer from the last reading when stopping this Driver, or 2: Deletes events after reading, and therefore does not save the pointer from the last reading when stopping this Driver because there is no need to store it

•Item: If the N2 parameter is equal to 0 (zero, Users Tags), inform the address and operation to perform by this Tag, with the following syntax:

<addressing space><address>[.<type>[<size of type>]][.<byte order>][/bit]

 

Available options for the Addressing Space parameter

 

The Address parameter is a number identifying the address of an item, register or bit, to read or write inside the defined addressing space. Values can be provided in decimal, hexadecimal, or octal format. For values in decimal, there is no need to add a prefix, or users can use the &d prefix. For values in hexadecimal, add the &h prefix, such as &hFFFF. For the octal format, use the &o prefix, such as &o843. This address may have an offset, relative to the address actually sent in a communication frame, which depends on the convention used by the manufacturer.

The parameters described next, on the other hand, are optional and used for extension to the default protocol or for compatibility with devices not fully adherent to protocol, also detailed later.

The Type parameter defines how bytes of a data area of a communication frame must be interpreted. If omitted, the default data types defined by the protocol are used for the functions in use, that is, Word for functions to access registers and Bit for functions to access digital data, Coils and Discrete Inputs.

Supported data types

 

The Size of type parameter is only necessary to specify for data types with variable size, such as BCD and String. The value of this parameter indicates the size of a data type, in bytes.

The Byte order parameter is a mnemonic indicating the order of bytes for number values. If this parameter is omitted, the protocol default is used, with the most significant bytes first in the communication frame, which is equivalent to b0, called Big Endian. The next table indicates which swap operations, that is, Swap Bytes, Swap Words, and Swap DWords, are performed for each sorting mnemonic, from b0 to b7.

Swapping operations

 

The Bit parameter allows returning a specific bit of an integer value, and it is obviously needed only in Modbus functions that return integer values, or Words. Usually, it is recommended to no use that feature, prefer an application's bit mapping. Bit 1 (one) is the least significant and, the greater the value, the more significant is that bit. The maximum allowed value obviously depends on the size of the data type, and it is currently 64 for Double data types. This parameter corresponds to the old Use Bit Mask option of number configuration.

When opening Tag Browser window, the main Tags offered by a device are already available, according to the next figure.