A-13
Appendices
CJ-series EtherNet/IP Units Operation Manual for NJ-series CPU Unit (W495)
A-4 Variable Memory Allocation Methods
App
A-4-1 Variable Memory Allocation Rules
Variables with Four-byte Alignments (e.g., DWORD)
Four bytes of memory are allocated for the four-byte alignment.
The location of the first byte of data in memory is an integer multiple of four bytes. Therefore, if a
variable with a two-byte alignment, such as WORD data, is inserted, two bytes of unused memory
will remain.
Example: Consecutive variables in the following order: DWORD, WORD, and DWORD
Variable Table
Name
A
B
C
Data type
DWORD
WORD
DWORD
Variable A,
4 bytes
Variable B,
2 bytes
Variable C,
4 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
Not used.
First byte +
(integer multiple of 2)
First byte +
(integer multiple of 4)
First byte +
(integer multiple of 4)
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