Each MELSEC A PLC can use one of four Transmission Control Protocol formats to communicate with its Mitsubishi Master, via RS-232.
ClearSCADA communicates with MELSEC A PLCs using Transmission Control Protocol Format 1.
For ClearSCADA to communicate with MELSEC A PLCs, set the Mode Setting switch on each PLC to indicate Protocol 1 (typically switch setting 1).
For more information, see the Mitsubishi documentation supplied with MELSEC A PLCs.