Beckhoff CU2508 Documentation page 59

Data representation on different platforms
Please note that simple and complex data (WORD, ARRAYs, REAL, STRING, user-defined struc-
tures) are represented internally in a different manner on different platforms! x86 platforms use
byte-alignment, others (ARM) 2-byte or 4-byte alignment.
This means that if a complex structure is created in an x86/PC PLC project and an ARM PLC
project, they can each have a different effective size and a different internal structure.
In Fig. Example for different size and structure in PC and CX, the structure in the CX (and hence
the network variable to be created there) is larger than in the PC; also the word and real variables
do not match each other because a variable can begin at any byte position in the PC, but only at ev-
ery even-numbered one in the CX.
Recommendation for structures that are identical on both end devices
- firstly, all 4-byte variables (must lie at an address that is divisible by 4)
- then all 2-byte variables (must lie at an address that is divisible by 2)
- then all 1-byte variables
Further recommendations
- if STRING(x) is used, the "EndOfString" zero is also interpreted as a character, otherwise x+1
must be divisible by 4
- the above rules also apply to sub-structures.
Please refer to the notes in the Structure section of the Infosys.
Use of Bus Terminal Controllers (BCxxxx, BXxxxx)
Since the representation of floating point numbers (REAL) on Bus Terminal Controllers (BCxxxx,
BXxxxx) differs from that in the x86, these cannot be transmitted. "SINT", for example, can be used
for signed values.
Fig. 80: Example for different size and structure in PC and CX
Settings in the System Manager
Appearance of the variables
Depending on the platform used (PC or EL66xx), the publisher/subscriber will appear differently. A
Publisher/Subscriber can be created.
• On a PC network interface, see Fig. Publisher settings - RT Ethernet
• on an EL66xx, see Beckhoff network variables - Settings [} 56]
The following settings options are available in the Beckhoff System Manager TwinCAT 2.10 build 1328:
Real-time Ethernet port multiplier Version: 2.6
Commissioning
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