Siemens SINUMERIK 840D sl Function Manual page 37

Signal flow
The following figure illustrates the signal flow for the digital NC outputs.
Overwrite mask
Every output that can be set by the NC part program can be overwritten from the PLC using
the overwrite mask. The previous "NC value" is lost.
The following sequence has to be carried out to overwrite the NC value from the PLC:
1. The relevant PLC interface output has to be set to the required signal status.
DB10 DBB6 or DBB132 ... (setting value of the digital NC outputs from the PLC)
2. The "setting value" becomes the new "NC value" when the overwrite mask for the relevant
output is activated (edge change 0 → 1).
DB10 DBB5 or DBB131 ...
This value remains operative until a new value is programmed (from the PLC or from the
part program).
Extended Functions
Function Manual, 10/2015, 6FC5397-1BP40-5BA3
A4: Digital and analog NC I/O for SINUMERIK 840D sl
2.2 Indirect I/O access via PLC
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