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Number of bytes allocated to the Ethernet IP Derived Data Type variable is increased randomly

Goals and Symptoms

Number of bytes allocated to the Ethernet IP Derived Data Type variable is increased randomly.

Facts and Changes

BMXNOC0401

Causes and Fixes


The number of bytes allocated to the Ethernet IP Derived Data Type (DDT) variable is increased by a
random number of bytes when the application is updated for the DTM configuration.

The extra bytes are created as a result of the input size/output size in the 'Group /Parameter' tab for
the Ethernet IP slave's 'General' properties being broken up into groups of 4 bytes. If the number of bytes
in the last group is less than 4, additional bytes are added to satisfy the byte boundary requirement. This
behavior works as designed because the M340 PLC is based upon a 4 byte data alignment. The additional
number of bytes can vary depending upon the input size/output size. The extra bytes are shown as the last
extra 'free( )' bytes in the DDT variables table..

i.e., If the 'Input size' and 'Output size' are both 10, the additional bytes would be 2 for
both the input and output DDT variable as shown below.



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