16 Chapter 1 wide range of utilities is available for configuring special function modules for the MELSEC System Q; there is no need to program special function modules, you just configure them. The package includes powerful editors and diagnostics functions for configuring MELSEC networks and hardware, and extensive testing and monitoring functions to help get applications up and running quickly and efficiently. It offers offline simulation for all PLC types and thus enables simulation of all devices and application responses for realistic testing. As another illustration, Siemens has SIMATIC STEP 7. This fully complies with the international standard IEC 61131-3 for PLC programming languages. With STEP 7, programmers can select from among various programming languages. Besides LAD and FBD, STEP 7 Basis also includes the IL programming language. Other additional options are available for IEC 61131-3 programming languages such as ST, called SIMATIC S7-SCL, or SFC, called SIMATIC S7-Graph, which provides an efficient way to describe sequential control systems graphically. Features of the whole engineering system include system diagnostic capabilities, process diagnostic tools, PLC simulation, remote maintenance, and plant documentation. S7-PLCSIM is an optional package for STEP 7 that allows simulation of a SIMATIC S7 control platform and testing of a user program on a PC, enabling testing and refining prior to physical hardware installation. By testing early in a project's development, overall project quality can be improved. Installation and commissioning can thus be quicker and less expensive because program faults can be detected and corrected early on during development. Likewise, Rockwell Automation manufactures RSLogix for the Allen-Bradley PLC-5 family of PLCs, OMRON has CX-One, and Telemecanique has ProWorx 32 for its Modicon range of PLCs. Summary A programmable logic controller (PLC) is a special form of microprocessor-based controller that uses a programmable memory to store instructions and to implement functions such as logic, sequencing, timing, counting, and arithmetic to control machines and processes and is designed to be operated by engineers with perhaps a limited knowledge of computers and computing languages. Typically, a PLC system has the basic functional components of processor unit, memory, power supply unit, input/output interface section, communications interface, and programming device. To operate the PLC system there is a need for it to access the data to be processed and the instructions, that is, the program, that informs it how the data is to be processed. Both are stored in the PLC memory for access during processing. The input/output channels provide isolation and signal conditioning functions so that sensors and actuators can often be directly connected to them without the need for other circuitry. Outputs are specified www.newnespress.com