Siemens CPU 31 Series Technical Data Manual page 243

Word and DWord access to the last valid addresses in an operand range
Word and DWord access to the last valid addresses in an operand range does not
result in a length-of-range error. If the initial address lies within the allowable ad-
dress range (E, A, M, L, D) but the final address lies outside this range, no length-
of-range error is generated in the module version (no synchronization error OB call
or CPU stop).
For access by Word and DWord, part of the addressed bytes can lie outside the
permissible range. Once access is completely outside the permissible range, a cor-
responding synchronization error is generated.
Example:
Access to a DB with 100 byte length (DBB0 to DBB99)
"T DBD 98" uses the addresses 98 to 101
Since the initial address is within the operand range, no length-of-range error is
generated.
However, the non-existent memory addresses 100 and 101 are also accessed.
The content of the non-existent memory area is undefined after access, and may
not be used by the user program.
This ensures data in other operand ranges is not overwritten during access.
Product Information on CPU319-3 PN/DP, 6ES7318-3EL00-0AB0
A5E00688649-02
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