A protocol tag is provided to receive data from PLC or to write data to PLC. To add a tag to a device/group, use the 'Add. Protocol Tag' command . .
The main tag settings:
Data region – a region of the variable interrogated. A region is a memory segment where a variable is stored. There the following regions:
•I – inputs
•Q – outputs
•M – memory cells
•DB – data blocks (DataBlock). The ’Optimized block access’ setting of DataBlock must be set off.
•T – timers (reverse reckoning of time remained by ms)
•C – counters (accumulated value)
•Access type – this parameter defines what method a tag uses for interaction with the variable: ReadOnly – only reading (the region I), WriteOnly – only writing (the regions Q,M,DB,T,C), ReadWrite – reading and writing (the regions Q,M,DB,T,C).
•Data type – data type of the variable interrogated in PLC. If this setting is changed, the Data type in server setting is automatically changed in the respective way.
•Block number – number of DataBlock where the variable interrogated is stored (only for the DB region)
•Byte address – address of a start byte of the variable interrogated
•Bit number – bit interrogated (for the BOOL data type)
•Count bytes - есif the data type is set to STRING or WSTRING, the setting determines the string size in bytes. Remember that one STRING character has a size of 1 byte, and WSTRING has a size of 2 bytes. Also, the beginning of the string contains service bytes which store the string length. For the STRING, 2 bytes are allocated for that, for the WSTRING, 4 bytes. Thus, the number of bytes for STRING equals LengthString+2 bytes, for WSTRING equals LengthString*2 + 4 bytes.
Other tag parameters are standard ones (see The Dialog of Tag Parameters ).