Siemens SIMATIC S7-1200

PLC concepts
5.4 Data types
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
135
Note
Valid data types that can be accessed by slice are Byte, Char, Conn_Any, Date, DInt,
DWord, Event_Any, Event_
Att, Hw_Any, Hw_Device, HW_Interface, Hw_Io, Hw_Pwm,
Hw_SubModule, Int, OB_Any, OB_Att, OB_Cyclic, OB_Delay, OB_WHINT, OB_PCYCLE,
OB_STARTUP, OB_TIMEERROR, OB_Tod, Port, Rtm, SInt, Time, Time_Of_Day, UDInt,
UInt, USInt, and Word. PLC Tags of type Real can
be accessed by slice, but data block tags
of type Real cannot.
Examples
In the PLC tag table, "DW" is a declared tag of type DWORD. The examples show bit, byte,
and word slice access:
LAD
FBD
SCL
Bit access
IF "DW".x11 THEN
...
END_IF;
Byte access
IF "DW".b2 = "DW".b3
THEN
...
END_IF;
Word access
out:= "DW".w0 AND
"DW".w1;
5.4.11
Accessing a tag with an AT overlay
The AT tag overlay allows you to access an already-declared tag of a standard access block
with an overlaid declaration of a different data type. You can, for example, address the
individual bits of a tag of a Byte, Word, or DWord data type with an Array of Bool.
Declaration
To overlay a parameter, declare an additional parameter directly after the parameter that is
to be overlaid and select the data type "AT". The editor creates the overlay, and you can
then choose the data type, struct, or array that you wish to use for the overlay.