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RSTi-OM User Manual
GFK-3212A
13.3
ISDU Handling
The IOLM provides a very flexible ISDU interface that is used by all supported industrial protocols. The
ISDU interface contains the following:
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13.3.1
ISDU Request/Response Structure
ISDU requests may contain a single command or multiple, nested commands. This subsection
discusses the following:
Single ISDU Command Request
This illustrates a single ISDU command request.
Figure 98: Single Command ISDU Request/Response
Functionality Descriptions
An ISDU request may contain one or multiple individual ISDU read and/or write commands.
Individual ISDU command-based byte-swapping capabilities.
Variable-sized command structures to allow access to a wide range of ISDU block sizes.
A single ISDU request may contain as many ISDU read and/or write commands as allowed by
the industrial protocol payload. For example, if an industrial protocol provides up to 500
bytes read/write payloads, then an ISDU request may contain multiple commands of various
lengths that can total up to 500 bytes in length.
For the ControlLogix family of EtherNet/IP PLCs, both blocking and non-blocking ISDU request
methods are provided.
The IOLM implements blocking ISDU requests by not responding to an ISDU request
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message until all commands have been processed.
The IOLM implements non-blocking ISDU requests by:
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Respond to an ISDU request message immediately after receiving and verifying the ISDU
request.
Requiring the PLC to monitor the ISDU request status with read messages. The IOLM will not
return a completed status until all of the ISDU commands have been processed.
Section 13
Jun 2021
136
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