Siemens S5-135U/155U - Manual (Page 195)

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System Manual
C79000-G8576-C199-06
For storage of your program, user memory in the form of RAM is integrated
on the board. You can store up to 64 x 2
10 bytes of code and data blocks here.
For data blocks, the CPU 928 additionally has an integrated DB RAM of 46 x
2
10 bytes.
Note
The DB RAM is loaded with DB/DX blocks when the user memory is full.
There is an interrupt line (IR) in the PLC for each CPU. It can be used when
the reaction to one or more events must occur with higher priority than the
reaction to other events.
To process a process interrupt, cyclic program processing is interrupted and
the program stored in OB 2 (OB for interrupt processing) is inserted. (Refer
to the CPU 928 Programming Guide for further details.)
This interrupt-driven program processing is only possible using an
interrupt-capable digital input module (e.g. 6ES5 432-...) or a CP/IP module
which operates in this way.
User Memory
Process Interrupt
Processing
CPUs, Memory Cards, Memory Submodules, Interface Submodules