User Manual

There are no specific rules related to the positioning of the DESIGO I/O modules or
their addresses. There is no requirement to allocate addresses contiguously and in
ascending order. However, when using the SIMATIC Manager for engineering, it is
important to engineer the I/O modules in ascending order of their P-bus addresses.
A maximum of 50 modules can be positioned in this way. Above this number, the
engineering tool rejects any further inputs.
If the overall system includes several DP slaves and additional S7 modules, the
positioning of the modules with the engineering tool can result in gaps in the address
space of a given DP/P-bus link. This depends on the order in which the individual DP
slaves are configured with modules, for example.
In such cases, the engineering tool ensures that consistent data structures are
transmitted when data is exchanged.
The option of modifying the allocated addresses manually must not be used. This
makes the data structures inconsistent at transmission time, which can lead to
unpredictable signal states at the outputs. It can also mean that the input signals are
wrongly assigned. Similarly, modules must not be moved after they have been
positioned in the list of module slots, as the engineering tool does not automatically re-
sort the address sequence.
Code-based diagnostics are used for trouble-shooting in the DP/P-bus link.
The LED
display also indicates the overall operational status
. Diagnostic options are available
both for individual modules and for the modules as a whole, for evaluation purposes.
Hardware list
The number of DESIGO I/O modules per DP/P-bus link depends on the following
conditions:
• Maximum 50 DESIGO I/O modules are supported
• Up to 128 load units
• Max. 216 input bytes
• Max. 216 output bytes
• The maximum total must not exceed 216 bytes
Refer to the section on Compatibility to determine the number of load units and bytes.
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Siemens Building Technologies DP/P-bus link CK1N9871en
Building Automation 23.04.2003