Omron SYSMAC CJ1W-EIP21, Operation Manuals

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Appendices
A-14
CJ-series EtherNet/IP Units Operation Manual for NJ-series CPU Unit (W495)
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Variables with Eight-byte Alignments (e.g., LWORD)
Eight bytes of memory are allocated for the eight-byte alignment.
The location of the first byte of data in memory is an integer multiple of eight bytes. Therefore, if a
variable with a two-byte alignment, such as WORD data, is inserted, six bytes of unused memory
will remain. If a variable with a four-byte alignment, such as DWORD data, is inserted, four bytes of
unused memory will remain.
Example: Consecutive variables in the following order: LWORD, WORD, and LWORD
Variable Table
Name
A
B
C
Data type
LWORD
WORD
LWORD
Variable A,
8 bytes
Variable B,
2 bytes
Variable C,
8 bytes
Bytes
Memory
First byte
First byte + 1
First byte + 2
First byte + 3
First byte + 4
First byte + 5
First byte + 6
First byte + 7
First byte + 8
First byte + 9
First byte + 10
First byte + 11
First byte + 12
First byte + 13
First byte + 14
First byte + 15
First byte + 16
First byte + 17
First byte + 18
First byte + 19
First byte + 20
First byte + 21
First byte + 22
First byte + 23
Not used.
First byte +
(integer multiple of 8)
First byte +
(integer multiple of 2)
First byte +
(integer multiple of 8)