Modbus TCP Configuration on IDEC FC6A Using WindLDR

Quick Answer

The FC6A with Ethernet capability supports Modbus TCP as both client (master) and server (slave). Configure the IP address in WindLDR, use the MSTR instruction for client operations, and enable the Modbus TCP server for SCADA access on standard port 502.

Modbus TCP vs Modbus RTU

Modbus TCP runs over Ethernet (TCP/IP) instead of serial (RS-232/RS-485). It uses the same function codes and register model as Modbus RTU but wraps the protocol in TCP packets. Modbus TCP supports multiple simultaneous connections and faster communication compared to serial Modbus.

Ethernet Configuration

In WindLDR, navigate to Communication Settings → Ethernet. Configure the FC6A IP address, subnet mask, and default gateway. Ensure the FC6A is on the same subnet as the connecting devices.

FC6A as Modbus TCP Server

Enable the Modbus TCP server in WindLDR Communication Settings. The FC6A listens on port 502 and responds to read/write requests from Modbus TCP clients. SCADA platforms like Ignition and Geo SCADA can connect as Modbus TCP clients to poll FC6A data.

FC6A as Modbus TCP Client

Use the MSTR instruction with TCP transport to read/write registers on other Modbus TCP devices. Specify the target IP address, port (502), function code, and register range.

Register Mapping

Same as Modbus RTU — R registers map to holding registers (R0 = 40001). M relays map to coils. This consistent mapping simplifies protocol transitions.

Troubleshooting

• Connection refused — verify IP address, port 502 open, server enabled
• Timeout — check network connectivity, switch/firewall settings
• Wrong values — verify register addressing and data type (16-bit vs 32-bit)