Siemens MOBY FC 56 Technical Description page 67

5.4 Programming Module Failure
Failure of a PROFIBUS module can be scanned with the PROFIBUS system
diagnosis.
However, when a failed slave is addressed by the FC 56, an I/O access error is
generated on the SIMATIC.
After this, the following occurs.
S OB 122 is called.
S If no OB 122 is programmed, the PLC assumes the STOP state.
The FC 56 has a routine which permits a "correct" error (error_FC = 09) to be
reported to the user when a MOBY PROFIBUS slave fails. The user then sets the
"ASM_failure = 1" bit in OB 122 for the failed MOBY channel. The following
example shows one way to implement OB 122.
Block: OB122
Segment: 1 Reset channel 1 when error occurs
L #OB122_MEM_ADDR
L "MOBY DB".SLG[1].ASM_address
-D
SRW 1
L 1
+D
L "MOBY DB".SLG[1].ASM_channel
==I
SPBN x1
SET
S "MOBY DB".SLG[1].ASM_failure
x1: NOP 0
OB 86 must also be available on the automation system in addition to OB 122 so
that the system does not assume STOP when a PROFIBUS slave fails. OB 86
does not have to contain code for the FC 56 to function correctly.
FC 56
J31069-D0155-U001-A0-7618
// Temporary OB 122 variable
// Formula:
// (#OB122_MEM_ADDR –
SLG[x].ASM_address) / 2 + 1
// Compare with conf. channel
// Power failure on ASM
Sample Applications
5-5