PLC commonly used in the introduction to the CPU and memory

CPU module is equivalent to the human brain and heart, it constantly collecting input signal, the execution of user programs, the output of the refresh system; The memory used to store programs and data. The CPU chip CPU module is mainly composed of CPU and memory. PLC using the following categories: CPU chip ( 1) Common microprocessors, such as Intel 86 to Pentium 8086801 series chips; ( 2) Single chip microprocessor ( Single chip microcomputer) , such as Intel MCS51/96 series single chip microcomputer; ( 3) Slice microcontroller processor, such as 2900 series slice decay processors AMD. PLC memory is divided into system program memory and user memory. System program is equivalent to a personal computer operating system, it make the PLC basic intelligence, able to complete the PLC various work prescribed by the designer. System programming by PLC manufacturers design and curing in ROM, users can directly read. The PLC user program designed by the user, it determines the input signal of the PLC and the specific relationship between the output signal. The user program memory capacity of the general with word ( Every word is composed of 16 bit binary number) For the unit, mitsubishi FX series PLC step calls the user program memory unit ( Step, the word) 。 Small PLC user program memory capacity in lK words left and right sides, large PLC controller on the number of the user program memory capacity is M ( Trillion) Words. PLC used the following kinds of memory: ( 1) Random access memory: ( RAM) Users can use the programmer to read the contents of the RAM, and the user program can be written to RAM, so RAM also called read/write memory. It is non-volatile memory, after its power disconnected, the information stored will be lost. RAM of high operating speed, low price, convenient. In order to shut off the PLC after external power supply, save the user program and some of the data in RAM ( Such as counter count) , for the RAM is equipped with a lithium battery. Now some PLC still use RAM to store the user program. Lithium battery can use 2 ~ 5 years, need to replace the lithium battery, PLC panel 'battery voltage is too low' leds light, at the same time there is an internal flag bit into l state, it can be used normally open contacts to turn on the control panel on the front panel indicator light or sound and light alarm, notify the user timely replacement of lithium battery. ( 2) Read-only memory ( ROM) The content of the ROM can only read, can't write. It is a volatile, its power supply disappears, still can save storage content. ROM— Used to store the PLC system program. ( 3) Electric erasing an EPROM ( EEPROM or E2PROM chips was introduced. ) It is a volatile, but can use programmer programming to it, both the ROM and nonvolatile RAM random access advantages. But the time needed for written information is much longer than RAM, EEPROM used to store the user program. Some basic configuration, PLC will EEPROM memory some PLC will EEPROM memory optional parts.
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