MC (MELSEC Communication) is the protocol for talking to Mitsubishi PLCs. inSCADA supports it over two transports, in the client role only.
Protocol value Transport MC TCPTCP MC UDPUDP
Their configuration fields are identical ; only the transport differs. TCP keeps the connection open and recovers a lost packet itself; UDP gives lower latency but a lost packet means the value simply does not arrive that cycle.
Parameter Default Description Frame Type — FRAME_1E, FRAME_3E or FRAME_4EPLC Type — A, QNA, Q, L or RTimeout (ms) 3000 The request timeout Connect Timeout (ms) — The connect timeout Retries — How many retries (1 – 10) Monitoring Timer — The PLC’s monitoring timer (0 – 65535)
On a directly connected PLC these are left at their defaults; they matter only when reaching another station across a network.
Parameter Range Description Network 0 – 255 The network number PC Number 0 – 255 The station number Destination Module IO 0 – 65535 The target module’s I/O number Destination Station 0 – 255 The target station
FRAME_1E is for the older A series; FRAME_3E and FRAME_4E are used on the Q, L and R series. Choosing a frame type that does not match your PLC gives a connection that establishes and then delivers no values — check which frame is enabled in the PLC’s Ethernet module configuration.
Parameter Description Scan Time The polling interval (at least 100 ms) Scan Type PERIODIC or FIXED_DELAY
A frame defines the range to read in PLC memory.
Parameter Description Device Code The memory area code Start Address The first device number Quantity How many points to read (1 – 960)
Code Code Code Code X inputY outputM internal relayD data registerB link relayW link registerR file registerZR file register (extended)L latch relayF annunciatorS stepV edge relaySM special relaySD special registerSB special link relaySW special link registerTS / TC / TN timerCS / CN / CC counterSTS / STN / STC retentive timerDX / DY direct I/OZ index
In MC the device number is entered as the PLC program writes it : hexadecimal for some device codes (X, Y, B, W among them) and decimal for others (D, M, R). Which applies depends on the device code and the PLC series together .
That is why the start address is a text field rather than a number — the field itself cannot know which base it is in. Enter it exactly as you see it in GX Works.
Parameter Description Type The data type Start Address The offset within the frame Bit The bit number (0 – 15), for bit access
Type Size BOOL1 bit INT16 / UINT1616 bit INT32 / UINT3232 bit FLOAT32-bit floating point
