With the help of direct addressing inputs, outputs and the data area can be read and written directly via the address. In some situations you can simplify the Grafcet enormously: For example, if 8 Boolean symbols are combined with AND in a transition. This can be simplified if only the byte in which the Boolean symbols are stored is checked for the value 255.
Access | Syntax | Example |
---|---|---|
Bit access | %D{Byte Address}.{Bit Address} | %D2.2 |
Byte access | %DB{Byte address} | %DB5 |
Word Access | %DW{Byte Address} | %DW8 |
Double word access | %DD{byte address} | %DD10 |
The correct address for a certain symbol can be found in the symbol table in the column "DB address":
**Example 1*: Reset several output symbols via a write command: It is much shorter to set a byte or word** to "0" in an action than 8 or 16 Boolean symbols. In the next sample the byte address of the first 8 Boolean outputs is "25". See picture:
Via a stored action upon activation that is connected to an initial step, all 8 outputs are initially set to '0':
Example 2: Compare whether at least 1 symbol has the state '1'.
If you want to check if at least 1 symbol has the state '1', you can e.g. check 8 symbols simultaneously via a byte access.
The two transitions (left and right in the following picture) are triggered by the same condition. All inputs have byte address 0.
Note: If symbols are addressed directly, there is a risk that the address of the symbol will change. If you insert new symbols into the symbol table, note that the direct addressing may have to be adapted.