Modicon M340 Plc Page 2-12 Communication

2/12 Functions (continued) I/O Scanning service The I/O Scanning Service is used to manage the exchange of remote I/O states on the Ethernet network after a simple configuration operation, with no need for special programming. I/O scanning is performed transparently by means of read/write requests according to the Modbus client/server protocol on the TCP profile. This principle of scanning via a standard protocol enables a device with the I/O Scanning service to communicate with any device supporting Modbus TCP messaging in server mode. This service can be used to define: b A word zone reserved for reading inputs b A word zone reserved for writing outputs b Refresh periods independent of the PLC scan During operation, the module: b Manages TCP connections with each remote device b Scans devices and copies the I/O to the configured word zone b Feeds back status words used to check that the service is working correctly from the PLC application b Applies pre-configured fallback values if a communication problem occurs A range of hardware and software products is available enabling the I/O Scanning protocol to be implemented on any type of device that can be connected to the Ethernet network (please consult the Modbus-IDA website: www.modbus-ida.org. Characteristics b Each Modicon M340 station can exchange a maximum of 100 words for writing and 125 words for reading. b Maximum size in the Modicon M340 PLC that manages the service (64 stations max.) with BMXNOE0100/0110 and BMXNOC0401 network modules: 2 Kwords (input) and 2 Kwords (output). I/O Scanning service diagnostics I/O Scanning service diagnostics can be performed in one of five ways: b Via the application program from a specific PLC data zone b From the setup software debug screen b From the PLC system diagnostic function displayed by means of an internet browser on a PC station b Using standard SNMP manager software Functions (continued) 2 Device with Modbus TCP messaging in server mode Modicon M340 automation platform Ethernet Modbus/TCP network Ethernet Modbus/TCP communication services 1 Modicon M340 device with I/O Scanning service INPUT OUTPUT + INPUT OUTPUT + A B A B 2 1 2 Word table Read Write Ethernet Modbus/TCP Input words Output words of devices Processors: page 1/8 Ruggedized Modicon M340 modules: page 3/2 2 1 3 4 5 6 7 8 9 10 2 1 3 4 5 6 7 8 9 10

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