Link Communication; Link Variables - Siemens SINUMERIK 840D sl Function Manual

B3: Several operator panels connected to several NCUs, distributed systems - only 840D sl

2.8 Link communication

2.8 Link communication
2.8
2.8.1

Link variables

Function
Complex systems often feature multiple NCUs, each with multiple channels. Each NCU has
a link communication channel for the purpose of coordinating manufacturing processes
throughout the entire system. Using this, each of the NCUs can exchange data cyclically with
every other NCU in the link grouping.
The link communication channel is based on a memory area on each NCU known as the link
variables memory. The user/machine manufacturer can define both the size and data
structure of the link variables memory on a system-specific basis. The data stored in the link
variables memory is addressed by what are known as link variables;
these are system-global user variables which can be read and written in part programs and
cycles by all NCUs involved in a link grouping if link communication has been configured.
Unlike global user variables (GUD), link variables can also be used in synchronized actions.
On systems without an NCU link, link variables can be used as additional global user
variables alongside standard global user variables (GUD).
Requirements
The following requirements must be met in order to use link variables for cross-NCU data
exchange:
● The link grouping must be installed and configured. See "Configuration of a link grouping
● Link communication must be activated:
Properties of the link variables memory
Assigning parameters for the memory size
The size of the link variables memory in bytes is set by means of the following machine data:
MD18700 $MN_MM_SIZEOF_LINKVAR_DATA (size of the NCU link variables memory)
The setting for the size of the link variables memory should be identical for all NCUs involved
in the link grouping. If the memory sizes are different, the largest value assigned is used.
Initialization
After an NCU is powered up, the link variables memory is initialized with 0.
Structure
From the point of view of the system, the link variables memory is an unstructured memory
area that is available for link communication purposes. The link variables memory is
structured by the user/machine manufacturer alone. Depending on how the data structure is
defined, the link variables memory is accessed by means of data format-specific link
variables.
168
(Page 174)".
MD18780 $MN_MM_NCU_LINK_MASK (activation of NCU link communication)
Function Manual, 09/2009, 6FC5397-1BP20-0BA0
Extended Functions