Operation With Process Alarm Via Interrupt - Siemens S5-155U System Manual

Operation with process
alarm via interrupt
Scanning the process inputs
System Manual
C79000-B8576-C199-03
To operate the 432 digital input module with process alarm via an
interrupt, you must either operate it in the CC where only certain slots
have interrupt lines (see Chapter 4), or in an interrupt-capable EU
connected to the CC with IM 307 - IM 317 interfacing (see also the
IM 307 - IM 317 manual). In the CC, you may only operate the
module in this mode at slots with an interrupt line (interrupt source).
So that the module can initiate a process alarm for a change of logic
state, the alarm must be processed by an alarm routine (alarm OB) in
the user program, with automatic acknowledgement of the alarm. To
avoid loss of an alarm, it must not be possible for the alarm OB to be
interrupted by process alarms. The CPU must process the process
alarms with level triggering (see Programming Guide of the CPU).
Example:
Program the following operations in the corresponding alarm OB:
L PW132
T FW10
L PW134
T FW12
Only the flag word may be accessed during the cyclic program.
Accessing the I/O bytes in the process image will result in alarm loss.
Addressing of the module must therefore be above address 127.
Double accessing of I/O bytes, even from different CPUs, is not
permissible (alarm loss).
The four I/O bytes of a module must be scanned successively and in
ascending order. The scanning of byte n inhibits all input circuits of
the module, and the scanning of byte (n + 3) enables them again.
Technical Description
(load I/O word)
(transfer flag word)
etc.
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