Commissioning PLX32-EIP-MBTCP: Subnets, Registers, and RPI
A commissioning checklist for the ProSoft PLX32-EIP-MBTCP covering subnet separation, register contracts, EtherNet/IP timing, failure tests and replacement records.
The ProSoft PLX32-EIP-MBTCP translates data between EtherNet/IP and Modbus TCP/IP. It does not create the data contract for you. Commissioning succeeds when subnet design, register mapping and update timing are documented before controller logic is released.
Keep the two Ethernet ports on different subnets
ProSoft specifies two independently addressed Ethernet ports. Each protocol can remain on its own subnet. Do not assign both ports to the same IP network.
Record both addresses, subnet masks and gateways. Also record which port carries EtherNet/IP and which carries Modbus TCP/IP. This prevents replacement work from becoming a network-discovery exercise.
Build the register contract before tags
Define every exchanged value in a register map. At minimum, record:
- Data direction.
- Modbus function code and starting address.
- Word count and data type.
- Byte and word order.
- Engineering units and scaling.
- Expected update rate.
- Behavior when communication fails.
The gateway provides up to 10,000 16-bit registers. Capacity does not remove the need for ownership rules. Reserve ranges for commands, status, alarms and diagnostics.
Match EtherNet/IP connections to the process
The gateway supports two Class 1 I/O connections. Separate fast control data from slower status data when their timing requirements differ. Set each RPI from process need, not the lowest selectable value.
Before enabling outputs, confirm that the PLC tag layout matches the configured I/O connection sizes. A one-word offset can move every downstream value.
Test the failure states
A live data value is not enough evidence. Run controlled tests for these conditions:
- Disconnect one Modbus device and verify stale-data indication.
- Enter an invalid register address and confirm command-level diagnostics.
- Restart the gateway and verify configuration recovery.
- Disable the PLC connection and confirm outputs move to the intended state.
- Check signed, unsigned and floating-point values at known test points.
Trend a sequence counter or timestamp through both protocols. It reveals frozen data that still looks plausible.
Prepare for replacement
Save the ProSoft Configuration Builder project, firmware version, IP plan and register map. If an optional SD card is used, verify that its backup matches the running configuration.
For hardware details, see the PLX32-EIP-MBTCP product page. For broader device-side checks, read what to verify after receiving a Modbus TCP device.