Beckhoff CX8110, Manual

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Configuration
CX8110 38 Version: 1.4
6.5.3 Creating process data
Up to 512 bytes of input and output data or 256 variables can be exchanged via the EtherCAT slave
interface (X101, X102). The 512 bytes of input and output data cannot be created individually, since 512
variables are required for this.
To avoid an excessive number of links, it makes sense to store data in a data structure. Note that the data
structures used are processed differently on an x86 system and an ARM processor. For example, the ARM
processor always places WORD variables (2 bytes) on an even address and DWORD variables (4 bytes) on
an address that can be divided by 4.
Data structure sample:
byTest :BYTE;
udTest:UDINT;
Table 12: Data structure with BYTE and UDINT variables
ARM address ARM variable Address x86 ARM variable
Byte Offset 0 Byte Byte Offset 0 BYTE
Byte Offset 4 UDINT Byte Offset 1 UDINT
Sum: 8 bytes Sum 5 bytes
You can determine the length of a data structure on both systems using the command SIZEOF. If the length
of the data structure is different, this indicates that the data structure is unsuitable.
You can solve the problem by smarter arrangement of the variables or by using dummy variables.
Table 13: Data structure with dummy variables.
ARM address ARM variable Address x86 ARM variable
Byte Offset 0 Byte Byte Offset 0 BYTE
Byte Offset 1 BYTE (Dummy1)
Byte Offset 2 BYTE (Dummy2)
Byte Offset 3 BYTE (Dummy3)
Byte Offset 4 UDINT Byte Offset 4 UDINT
Sum: 8 bytes Sum 8 bytes
Create process data as follows:
1. Under Devices in the tree view on the left, right-click on Inputs to create input variables.