外文翻譯--可編程控制器-其他專業(yè)(存儲版)
【正文】 r supply is usually a separate module, and the I/O modules are separate from the processor. The types of I/O modules include discrete (on/off), analog (continuous variable), and special modules like motion control or highspeed counters. The field devices are connected to the I/O modules. Depending on the amount of I/O and the particular PLC processor, the I/O modules may be in the same chassis as the processor and/or in one or more other chassis. Up until the late 1980s, the I/O modules in a typical PLC system were in chassis separate from the PLC processor. In the more typical presentday PLC, some of the I/O modules are present in the chassis that contains the processor. Some PLC systems allow more than one processor in the same chassis. Smaller PLCs are often mounted on a DIN rail. The smallest PLCs (often called microPLCs or naonPLCs) include the power supply, processor, and all of the I/Os in one package. Some microPLCs contain a builtin operator interface panel. For many microPLCs, the amount of I/O is limited and not expandable. Basic software, memory architecture (IEC 611313) The IEC 611313 standard defines a memory and program model that follows modern software engineering concepts. This model incorporates such features as topdown design, structured programming, hierarchical anization, formal software interfaces, and program encapsulation. Fortunately, extensive training in software engineering techniques is not necessary to bee a proficient programmer. If fully implemented, the model is reasonably plicated. The main disadvantages of
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