User Memory; Process Interrupt Processing - Siemens S5-155U System Manual

CPU 928

User memory

Process interrupt
processing
5 - 34
You require a user memory submodule (RAM or EPROM) for storage
of your program. You can store up to 64 Kbytes of code and data
blocks here. For data blocks, the CPU 928 additionally has an
integrated DB RAM of 46 3/4 Kbytes.
Note
The DB RAM is loaded with DB/DX blocks when the RAM
submodule is full or an EPROM submodule is plugged in.
A description of the memory submodules can be found in Sections 5.6
and 5.7; order numbers are given in the ordering information.
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 an 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 suitably
operating CP/IP module.
System Manual
C79000-B8576-C199-03