Communication In Link Grouping - Siemens SINUMERIK 840D sl Function Manual

B3: Several operator panels connected to several NCUs, distributed systems - only 840D sl
2.10

Communication in link grouping

2.10
Although communication by means of link modules is high-speed communication, the
following aspects have to be taken into account during configuration.
Data transport
Both cyclic and acyclic services are used for data communication. The cyclic data area
ensures that the data are transferred in every interpolation cycle.
The acyclic service uses machine data, link variables and data for container rotation, for
example. If too many data were selected simultaneously for the acyclic link communication,
the transfer sequence is governed by an internally defined priority system. The actual
value/setpoint data for the lead link axis are transferred via the cyclic service.
Dependencies
The times for communication are determined by:
● Number of data for cyclic exchange
● Type and speed of the NCUs
● Link module speed (currently 12 Mbaud)
● Point-to-point protocol: The cyclic communication load increases sharply with each
The set interpolation cycle must be identical for all lead link NCUs in the axis grouping.
Link resources
The machine data below controls the assignment of send/receive buffers for link
connections:
MD18781 $MN_NCU_LINK_CONNECTIONS
A maximum of 32 buffers of this kind are available for each NCU.
One of these buffers is reserved on a priority basis for the setpoint/actual value transfer of a
link axis. Only the remaining ones can be used for acyclic data exchange (alarm, container
switch, link variable transfers). The maximum number of 32 must not be exceeded.
If the machine data below is set with 0, the software itself determines the requirement as 25
connections:
MD18781 $MN_NCU_LINK_CONNECTIONS
A value not equal to 0 explicitly defines the number of acyclic connections to other NCUs.
Extended Functions
Function Manual, 09/2009, 6FC5397-1BP20-0BA0
(number of link axes, number of lead link axes (see below), number of axes in a cross-
NCU container with high priority and number of link variables having to be exchanged in
each interpolation cycle)
additional NCU, as illustrated by the schematic diagram "Increase in communication time
with the number of NCUs connected via the link (for scaling refer to Interdependencies)".
2.10 Communication in link grouping
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