What Data Table Read and Write Mean
DATA_TABLE_READ and DATA_TABLE_WRITE are EtherNet/IP access patterns that determine whether a gateway or client reads values from a PLC data table or writes values back to it. In real projects, this is one of the easiest places to get a connection that looks healthy while still failing the actual control objective.
Direction Summary
| Mode | Direction | Typical Use |
|---|---|---|
DATA_TABLE_READ | PLC to gateway | Status values, measurements, read-only data |
DATA_TABLE_WRITE | Gateway to PLC | Commands, setpoints, writable values |
Why It Matters
- Read access does not imply write access.
- A project can look functional during basic testing while all command paths still fail.
- Point classification should happen before mapping starts, not after the first failed write test.
Common Mistake
[!WARNING] Using
DATA_TABLE_READfor points that must be writable is one of the most common EtherNet/IP setup errors. Reads succeed, the system appears alive, and the write problem is found late.
Practical Guidance
- Classify every point as read-only or read/write.
- Map writable points with the correct write-capable path.
- Test at least one known-good write during commissioning.