Siemens S7-200PLC series (1)
tool
As the saying goes: "Workers must first sharpen their tools if they want to do well." To understand and use Siemens PLC proficiently, you must first understand its programming software- step7 microwin v4.0 . The link is the download address of the software.
The installation of the software is binary, just follow the instructions, but it is recommended that the installation location of the software should be the default, and do not modify it to facilitate file search. So if possible, install a virtual machine. Does not affect future use.
hardware
The central processing unit (cpu)
is the core of the PLC. The main types are CPU221, CPU222, CPU224, CPU224xp, and CPU226. It has the following features:
1. Receive and store user programs and data input by programming tools, and display the content and storage address of the program on the display
. 2. Check and verify user programs. The user who is inputting is checked, and the grammar error is found, and the input is stopped immediately; if an error is found during the running of the program, the alarm is immediately reported or the execution of the program is stopped.
3. Receive and call on-site information. Save the data received on-site, call it out when the data is needed, and send it to the place where the data is needed.
4. Execute the user program. When the PLC enters the running state, the CPU reads, interprets and executes the programs one by one according to the sequence of user program storage, completes various operations specified in the user program, and sends the program execution structure to the output port to drive the outside of the PLC Load
5. Fault diagnosis. Diagnostic power failure PLC internal circuit, according to the type of fault or error, by corresponding display displays information to prompt the user to correct the error or time troubleshooting
memory
simply defined as: storing programs and data.
There are three main types: system program memory, user program memory, and working data memory
. 1. System program memory: controls the operation of the PLC and makes the PLC go normally.
2. User program memory: stores the user for specific control tasks, with RAM (with lithium battery Carry out power-down protection), EPROM, EEPROM.
3. Working data memory: to store working data, ON i.e. user program / OFF state, and other numerical data
input / output interface: main switch input and output and analog input and output
expansion interface: mainly used to add extensions Module
Communication interface: communication processing, serial interface and parallel interface
PLC peripheral equipment: meters, sensors, etc.
working principle
- CPU read input status
- Programs stored in the CPU use inputs to execute control logic. When the program is running, the CPU refreshes the relevant data
- CPU writes data to output
Operating mechanism
Simply put, it is the operating cycle:
1. Read input: S7-200 copies the state (digital and analog) on the physical input point to the input process influence register. When the analog quantity is input, if the analog quantity filter is enabled, otherwise the S7-200 will not refresh the analog quantity input value during the scan period. Analog filtering will get a stable signal (cpu224Xp has a converter to obtain the average value, no software filtering is required)
2. Execute logic control program: S7-200 executes program instructions and stores data in various storage areas (note the interrupt The use of the program, it is not executed as a part of the normal scan cycle, only executed when an interrupt event occurs)
3. Processing communication request: S7-200 performs communication tasks (cpu processing received from the communication port or intelligent I/O module any information to
4. the CPU performs self-diagnosis: check the S7-200 firmware, a program memory and expansion modules are working properly
5. write output: stored data is copied to the physical output point (analog output directly process image output register Refresh, has nothing to do with the scan period)