Siemens S5-135U/155U System Manual page 323

Only the flag word (FW) 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 the input circuit of the
module, and the scanning of byte (n + 3) enables them again.
Settings on the
Make the following settings on the module to operate it with a process alarm
Module
via IB 0:
Step
1
2
3
4
0
1
2
3
4
5
6
:OFF
7
:ON
Figure 8-5 Switch Settings for Operation with Process Alarm via IB 0 (Example)
System Manual
C79000-G8576-C199-06
Action
Insert jumpers X3 and X4
Set switch row S1 to Off.
Set bit 0 on switch row S2 to On, and all other switches to Off.
Set switch row S3 to choose whether the interrupt is to be initi-
ated with a positive-going (leading) or negative-going (trail-
ing) edge. The setting of a pair of switches applies to an entire
byte.
S1
S2
0
IR-A
1
IR-B
IR-C 2
3
IR-D
4
IR-E
5
IR-F
IR-G 6
INT 7
Digital Input/Output Modules
S3
0
Bit 0 }
1
Bit 1
2
Bit 2
}
3
Bit 3
4
Bit 4
}
5
Bit 5
6
Bit 6
}
7
Bit 7
Byte 0: Positive-Going Edge
Byte 1: Negative-Going Edge-
Byte 2: Both Edges
Byte 3: No Process Interrupt
Byte 3
Byte 2
Byte 1
Byte 0
8-11