What DATA_TABLE_READ / WRITE Is
DATA_TABLE_READ and DATA_TABLE_WRITE are EtherNet/IP access modes that determine how a gateway reads from or writes to PLC data tables via CIP messaging.
| Mode | Direction | Use |
|---|---|---|
| DATA_TABLE_READ | PLC → Gateway | Gateway reads values from the PLC |
| DATA_TABLE_WRITE | Gateway → PLC | Gateway writes values to the PLC |
The #1 Configuration Mistake
[!WARNING] Using DATA_TABLE_READ for points that require write access is the most common EtherNet/IP integration error. Writes fail silently — the gateway reads successfully, so the connection appears healthy, but setpoint commands never reach the PLC.
When to Use Each
| Point Type | Mode Required |
|---|---|
| Sensor readings, status values | DATA_TABLE_READ |
| Setpoints, commands, limits | DATA_TABLE_WRITE |
| Bidirectional values | Both — read one Assembly, write another |
Common write-required points include:
- Temperature setpoints
- Fan speed commands
- Enable/disable flags
- Limit values
- Schedule overrides
How to Avoid the Mistake
- Classify every point as read-only or read/write before starting configuration
- Map read points to DATA_TABLE_READ, write points to DATA_TABLE_WRITE
- Test write operations explicitly — don’t assume writes work just because reads succeed
See EtherNet/IP Integration Guide for a complete walkthrough.