Siemens S5-135U/155U appendix User Memory

CPUs, Memory Cards, Memory Submodules, Interface Submodules

User Memory	For storage of your program, user memory in the form of RAM is integrated
	on the board. You can store up to 64 x 210 bytes of code and data blocks here.
	For data blocks, the CPU 928 additionally has an integrated DB RAM of 46 x
	210 bytes.
	Note
	The DB RAM is loaded with DB/DX blocks when the user memory is full.

Process Interrupt There is an interrupt line (IR) in the PLC for each CPU. It can be used when

Processingthe 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.

System Manual	5-55
C79000-G8576-C199-06