Beckhoff EL6601 Documentation page 108

Commissioning
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. (see Fig.
"Data representation e.g. x86 Systems vs. ARM Systems")
In the sample, 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 every even-numbered one in the CX.
Consequences
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.
Consequences
Use of Bus Terminal Controllers (BICxxxx, 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 sample, can be used
for signed values.
Fig. 128: Data representation e.g. x86 Systems vs. ARM Systems
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 [} 105]
The following settings options are available in the Beckhoff System Manager TwinCAT 2.10 build 1328:
108 Version: 4.2 EL6601, EL6614