The working process of the programmable controller and FN2N PLC

Though PLC has many characteristics of microcomputer, but the way it works with microcomputer are quite different. Microcomputer generally adopt the wait command works, such as common keyboard scanning mode or I/O scanning mode, a key press or I/O action is transferred to the corresponding subroutine keyless press continued to scan. Circular scanning mode, PLC is used in the PLC user program in order to deposit, such as: 1 x x x x x x x x 2 3 10 x x x x x x x x 11 EDCPU from the first instruction execution procedures, until the end and then return to the first. So the cycle cycle. This way of working is under the control system software, progressive scanning state of each input point processing according to the user program, and then order to output a corresponding control signals. The whole working process can be divided into five stages: self-diagnosis, communication with the programmer and so on, the input sampling, user program execution, and the output refresh, its working process diagram as shown: PLC working process diagram 1) Every time before scanning the user program, are to implement fault self-diagnosis procedures. Self-diagnosis for part I/O, memory, CPU, etc. , found that abnormal downtime display error. If the diagnosis is normal, continue to scan down. 2) PLC to check whether there is a request with the programmer and computer communication, if have the corresponding processing, such as receiving by the programmer procedures, commands, and from a variety of data, and to show the status, data, such as error message sent to the programmer for display. If there is a request of communication, such as computer, also in this period of time to complete the data receiving and sending. 3) The PLC controller CPU for each input scan, a state on the input side to input in the status register, this is the input sampling stage. 4) The central processor CPU will command to bring up and carry out a detailed, to the right people and lose the original output state ( These states are collectively referred to as data) 'Processing', that is, according to the procedure of data logic, arithmetic, and then send the correct results to output in the status register, this is the program execution stage. 5) When finished all the instruction execution, concentration in the status register of the output through the output components into the control device can accept voltage or current signal, to drive the charged equipment, this is the output refresh stage. The working process of the PLC through the five stages, called a scan cycle. Again after completion of a cycle to perform the above process, scanning cycle. Is one of the important indicators of PLC scan cycle, without considering the second factor ( Communicate with programmer, etc) When scanning period T as follows: T = ( Read a bit of time x input points) + ( Speed x steps program) + ( The output time x output points) Ten fault diagnosis time obviously scanning time mainly depend on the length of the program, generally can scan more than dozens of times per second, that there is no effect for industrial equipment usually. But for more strict control of time, fast response speed requirements of system, the response time should be accurate calculation, careful procedures, reasonable arrangement of the order of the instruction, to minimize impact as well as the response latency of scan cycle. PLC and relay contactor control is one of the important differences between the work in a different way. Relay contactor control is to work in a 'parallel' way, that is, at the same time in accordance with the way to work, as long as the formation of a current path, there may be several relay action at the same time. And PLC is repeatedly scan the type of work, it is to continuous cycle to perform a detailed program, at any moment it can only execute one instruction, this means that the PLC is a 'serial' way to work. The serial works can avoid the contact of the relay contactor control competition and timing mismatch problem. In a word, using circular scanning approach is also the biggest characteristic of PLC from the microcomputer, the user should pay special attention to. FN2N specification and composition of PLC controller FN2N series PLC has FN2N16, FN2N32, FN2N48, FN2N64, FN2N80, FN2N128 FN2N 32, mainly from the following several parts: 1, the control unit: equipped with programming, computer interface, with the expansion of the I/O expansion unit is connected to the mouth, input and output terminals, power input and output terminal, FN2N has 16 inputs and 16 output points. 2, extension units. 3, intelligent unit. Unit 4, link. 5, programming tools: use MELSOFT GX Developer programming software.
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