What Assembly Objects Are
Assembly Objects are the EtherNet/IP and CIP containers used to group I/O data for exchange between devices. Each assembly is identified by an instance number and a fixed data size, and scanner-side configuration depends on those details being correct.
In practical work, Assembly Objects are one of the first places an EtherNet/IP integration fails. A healthy network path does not help if the instance numbers or expected byte counts are wrong.
Why They Matter
- They define how cyclic I/O data is packaged.
- They determine what a PLC or scanner expects to read from and write to.
- Wrong assembly assumptions create silent offset problems or outright connection failures.
Common Naming Pattern
| Name | Direction | Practical Meaning |
|---|---|---|
DataFromDevice | Device to scanner | Input data produced by the EtherNet/IP device |
DataToDevice | Scanner to device | Output data written toward the EtherNet/IP device |
[!NOTE]
DataFromDevicemeans data coming from the field device, which typically appears as scanner inputs.
Configuration Inputs
Each Assembly Object setup normally requires:
- Instance number
- Exact byte size
- Direction and ownership
- Matching scanner-side configuration
Common Problems
- Byte size mismatch between scanner and device
- Wrong instance number selected
- EDS file assumed to be correct when the installed firmware differs
- Data table or I/O direction assumed incorrectly