Description of Components
2-5
DP/PA Link and Y Link Bus Couplings
A5E00193841-011
2.4 DP/PA link
The DP/PA link is intended for the following applications:
S7 standard mode on the S7-300 or S7-400
Redundancy mode on the S7-400H
DP standard master mode
Some of the following details apply to both the S7 standard mode and to the DP
normal master mode. In these cases, the term “non-redundant operation” is used.
Operating principle
On the higher level DP master system, the DP/PA link is a DP slave and acts
as a proxy for the nodes connected to the underlying bus system (PA field
devices).
The DP/PA link forms an independent underlying bus system that is decoupled
from the higher level DP master system with respect to communication.
The use of several DP/PA couplers increases the current carrying capacity of
the PA master system.
Together with the connected PA field devices, the DP/PA couplers of a DP/PA
link form a single common bus system.
Configuration options
DP/PA links can be used to extend a DP master system as follows:
The number of DP/PA links on a DP master system is only limited by the
maximum number of bus nodes of 126.
Up to five DP/PA couplers can be operated in each DP/PA link. Y couplers
cannot be operated in the DP/PA link.
The number of nodes in each PA 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 DP/PA link are both
derived from the frame contents of the underlying PA field devices.
The maximum length of the frames for configuration data, parameter
assignment data, diagnostics data and I/O data is 244 bytes in each case.
Configuration
The DP/PA link can be configured with STEP 7 as of V5.2.
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