Siemens SINUMERIK 840Di Function Manual page 1241

The figure below shows the structure of the M decoding according to list:
Fig. 2-14 M decoding acc. to list
Activation of the function
The number of evaluating/decoding groups is indicated in the basic program parameter
"ListMDecGrp" when FB1 is called in OB 100 (see also FB1 description). M decoding is
activated if this value is between 1 and 16. Before the function is activated, the decoding list
DB75 must be transferred to the PLC followed by a restart.
Structure of decoding list
The source file for the decoding list (MDECLIST.AWL) is supplied with the basic program.
DB 75 is created when the STL source is compiled.
There must be an entry in decoding list DB 75 for every group of M functions to be decoded.
A maximum of 16 groups can be created.
16 bits are available in each group in the list of decoded signals.
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
2.7 Structure and functions of the basic program
Detailed Description
2-47