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Design, Functions and Operation
Program Memory (EPROM/RAM)
In order to safely store the control program outside of the PLC, you must store it on an EPROM or
EEPROM memory submodule.
Programs that are available on a memory submodule (EPROM) can be copied to the internal
program memory. This internal program memory is a reserved area of the CPU's internal RAM
memory.
The internal RAM memory has the following characteristics:
•
The memory contents can be changed quickly.
•
Memory contents are lost when there is a supply voltage failure and there is no battery backup.
Operating System (ROM)
The operating system contains system programs that determine how the user program is executed,
how inputs and outputs are managed, how the memory is divided, and how data is managed.
The operating system is fixed and cannot be changed.
Process Images (PII, PIQ)
Signal states of onboard inputs, onboard outputs, and output modules are stored in the CPU in
"process images". Process images are reserved areas in the CPU RAM. During correct operation,
the operating system ensures that the process images of both basic units are identical.
Input and output modules have the following separate images:
•
Process image input table (PII)
•
Process image output table (PIQ)
Serial Interface
You can connect programmers, operator panels and monitors at the serial interface (cable
connector). Via the serial interface, you can connect both controllers as slaves to the SINEC L1
local area network.
Timers, Counters, Flags
The CPU has timers, counters and flags available internally that the control program can use.
The program can set, delete, start and stop the timers and counters. The time and count values are
stored in the reserved areas of the RAM memory.
There is another area in the RAM memory where information such as intermediate results can be
stored as flags. You can address the flags by bits, bytes, or words.
If battery backup is available, then some of the flags and counters remain in the internal RAM
memory even if the supply voltage fails or the controller is switched off. These flags and counters
are retentive.
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