Most of the user programs of programmable logic controllers are stored in the RAM that uses lithium batteries as backup power. Within the specified time (generally within five years), the lithium battery must be replaced quickly within the specified short period of time. (Generally within 10 seconds). In general, this storage method is very safe.
However, in an environment with strong interference, the user program in RAM (Allen Bradley 1734-AENTR Ethernet Communication Module, Siemens 6ES7331-7HF01-0AB0 SIMATIC S7-300 Analog Input Module, Allen Bradley 1756-L71 Logix5571 Processor, B&R X20DI4371 Digital Input Module)may also be rewritten or flushed, which is of course very rare. If the voltage of the lithium battery protecting the user program in the RAM is lowered, if the battery is not replaced in time, the user program in the RAM will also be lost. For systems with particularly high reliability requirements, after the user program is debugged, it can be written into EPROM or EEPROM that will not be lost even if the lithium battery is not used to protect the program after power off. Writing the program into EPROM requires a more expensive dedicated The writer generally chooses the EEPROM that can be written into the program by the programmer. When the system is running, the EEPROM should be write-protected to prevent it from being disturbed or artificially rewritten.
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