Description of Components
2-8
DP/PA Link and Y Link Bus Couplings
A5E00193841-011
2.5 Y link
The Y link is only intended for use in the redundancy mode on S7-400H.
Operating principle
On the higher level DP master system, the Y link is a DP slave and acts as a
proxy for the nodes connected to the underlying bus system (DP slaves).
The Y link forms an independent underlying bus system that is decoupled from
the higher level DP master system with respect to communication.
Configuration options and limitations
Y links can be used to extend a redundant DP master system as follows:
The number of Y links on a S7-400H is only limited by the maximum number of
bus nodes of 126.
Only one Y coupler can be operated per Y link. DP/PA couplers cannot be
operated in the Y link.
The number of nodes in each underlying DP master system is limited to 64. The
sum of slots (see Section 10.2.2) is limited to (236 – number of PA slaves) in
each case.
The configuration frame and the user data frame of the Y link are both derived
from the frame contents of the underlying slaves.
The maximum length of the frames for configuration data, parameterizaton
data, diagnostics data and I/O data is 244 bytes in each case.
It is not permissible to cascade Y links.
A direct exchange of data and synchronicity is not possible in the underlying DP
master system.
Configuration
The Y link can be configured with STEP 7 as of V5.2.
For the calculation of bus parameters by STEP 7, the nodes connected to the
underlying DP master system and the Y link itself are included in the calculation.
Slaves on the underlying DP master system are only operated in the DPV1 mode if
they are suitable for a bumpless switchover when a system change takes place
during operation.
STEP 7 can identify a slave’s suitability by an entry in its device master file:
PrmCmd_supp=1
If this entry is not present, the slave is operated in DPV0 mode.
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