Thursday, May 5, 2011

Software Driver for PLC Micro





Schneider Modicon PLCs already chosen by the hardware engineers at NSLS. The decision was based on the different networking options, cost, technical support, the availability of software tools for the PLC logic development, and a wide range of inexpensive I/O modules availability. The first project on the controls of power supply used TSX Quantum Controllers. The logic is saved and operated in the processor of Quantum. A module of Ethernet linked to the processor through quantum-back-plane offers the link to the control system. Current projects utilize the processors from the family of TSX Momentum, which consist of processor adapters, communication adapters and option adapters. Various I/O modules are used. The PLC-CPU corresponds with the I/O modules via the Modbus Plus network or IO-bus.

The difficulty and variety of various hardware units build each micro unique but the software of real-time in the standard interface of micro presents to the programs high-level. They access the signals of hardware by identifiable names. A READ set commands is used to get data from the hardware. A WRITE set commands controls the hardware. The PLC micro luxuries as a unit of intelligent slave with the communication link are Ethernet. Modbus-TCP/IP is the communication protocol used over the Ethernet, which mainly drives in a MODBUS frame into the frame of TCP/IP standard.

A driver of software has been built up to PLCs interface with a micro. The driver raises a client task, which opens a TCP relation to the specific PLC server and transmits the requests of Read Multiple Registers occasionally to acquire data from the PLC. The driver carries multiple clients. If the PLC connection is off-line, the software will report the error to the Control Room, secures the current connection and redo. The modules of application in the micro correspond with the client jobs by the utility functions built in the driver.



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