輸送、均勻鋪料設備控制系統畢業論文(編輯修改稿)

　

【文章內容簡介】 the program and identify programming problems.Debugging aids such as first and multiple scan functions can be used in STOP mode, and result in a STOP to RUN mode change for the prescribed number of scans.Fatal errors are stored by the PLC operating system and force a mode change from RUN to STOP mode. If the PLC has detected a fatal error, a mode change from STOP to RUN is not allowed while the fatal error condition persists. Nonfatal errors are stored by the PLC operating system function and are available for inspection, but they do not cause a mode change from RUN to STOP.In STOP mode, the PLC is in a semiidle state. Execution of the user program is discontinued。 input updates are performed。 user interrupt conditions are disabled. The following diagram depicts the timeline that the PLC follows in the STOP mode.In the event that munication interrupts are occurring, the PLC receives the messages and executes the requests as appropriate. While the PLC remains in the STOP mode, I/O value changes are made to the image register. One exception to this is the force function that overrides I/O value changes to the image register. While in STOP mode, you are able to load, upload, or delete the user program memory.In the event that one or more devices are trying to municate with the PLC through the munication port, the PLC responds to each request in turn. The PLC does not attempt to prevent the actions of one municator from interfering with the actions of another municator. All necessary precautions to guard against such interference must be provided by your system design.Selfdiagnostic checks include periodic checks of the operating system EEPROM, I/O module status checks and I/O expansion bus integrity check performed on each access to expansion I/O.In RUN mode, the PLC reads inputs, executes your program, writes outputs, responds to munications requests, updates intelligent modules, performs internal housekeeping chores, and responds to your interrupt conditions. Fixed scan times for the RUN mode execution cycle are not supported by the PLC. These actions (except for your interrupts) are serviced according to priority in the order in which they occur. This execution cycle is called the scan cycle and is shown below.Each scan cycle begins by reading the current value of the input bits and writing these values to the input image register. Input bits having no corresponding physical input, but which are in the same byte as bits with physical inputs, are zeroed in the image register on each input update cycle, unless they are forced.After reading the inputs, your program executes starting with the first instruction and proceeding until the end instruction. Upon reaching the end instruction, the PLC checks to see if the intelligent modules of the system need to be serviced. If they do, then the message is read and buffered for the next phase of the cycle.During the message processing phase of the scan cycle, messages that have been received from the munications port are processed. Completed responses are set aside for transfer to the munications requester at the appropriate time.Selfdiagnostic checks include periodic checks of the operating system EEPROM and the user program memory as well as I/O module status checks.Finally, the output image register values are written to the output modules. This pletes one scan cycle.SIMATIC LAD InstructionsBit Logic Clock Communications Compare Convert Counters FloatingPoint Math Integer Math Interrupt Logical Operations Move Program Control Shift/Rotate String Table Timers Call SubroutinesENO UsageENO is a Boolean output for boxes in LAD and FBD. ENO allows you to connect boxes in series (horizontally) rather than in parallel (vertically). If the box has power flow at the EN input and the box executes without error, then the ENO output will pass power flow to the next element. In the event that an error is detected in the execution of the box, then power flow will be terminated at the box that generated the error.ENO has the same status image as EN (EN=ENO), unless the operation does not execute correctly. For example, the DIV_I instruction provides ENO=0 for a divide by zero.In STL there is no ENO output, but the STL instructions that correspond to the LAD and FBD instructions with ENO outputs do set a special ENO bit. This bit is accessible with the STL instruction AENO (AND ENO) and may be used to generate the same effect as the ENO bit of a box.Direct and Indirect AddressingWhen you write your program, you can use either of three modes of addressing instruction operands:Direct Symbolic Indirect Direct AddressingThe S7200 stores information in different memory locations that have unique addresses. You can explicitly identify the memory address that you want to access. This allows your program to have direct access to the information. Direct addressing specifies the memory area, size, and location。 for example, VW790 refers to word location 790 in V memory area. To access a bit in a memory area, you specify the address, which includes the memory area identifier, the byte address, and the bit number preceded by a period. The figure below shows an example of accessing a bit (which is also called addressing). In this example, the memory area and byte address (I = input, and 3 = byte 3) are followed by a period (.) to separate the bit address (bit 4).You can access data in most memory areas (V, I, Q, M, S, L, and SM) as bytes, words, or double words by using the byteaddress format. To access a byte, word, or double word of data in the memory, you must specify the address in a way similar to specifying the address for a bit. This includes an area identifier, data size designation, and the starting byte address of the byte, word, or doubleword value, as shown in the figure below.Data in other memory areas (such as T, C, HC, and the accumulators) are accessed by using an address format that