Siemens SINUMERIK 840D sl Function Manual page 229

Supplementary conditions
1. For a communication error, the following system variables are always set independent of
the error response set using the system variable $A_FSDP_ERR_REAC:
$A_FSDP_ERROR = 1
$A_FSDP_SUBS_ON = 1
2. When a communication error occurs, the currently programmed error response is realized.
If the error response is changed, it only becomes effective when the next communication
error occurs.
3. Whether STOP D or STOP E is initiated as error response can be parameterized using:
NCK: $MN_SAFE_SPL_STOP_MODE
PLC: DB18.DBX36.1
4. The system variable $A_FSDP_ERR_REAC[1...n] is a part of the crosswise data
comparison SPL-CDC.
Note
Until the system variable is programmed for the first time, after the control boots, the value set
using MD $MN_SAFE_SDP_ERR_REAC is active.
Output data, F_SENDDP
System variable: Error signal, $A_FSDP_ERROR
System variable $A_FSDP_ERROR[1...n] is used to indicate that there is a communication
error. The specific cause, determined by F_SENDDP, is communicated using the diagnostics
data (system variable $A_FSDP_DIAG).
The system variable $A_FSDP_ERROR is cyclically compared with the corresponding PLC
variables FSDP[1...3].ERROR. If unequal, there is a system error and this is displayed using
Alarm 27355 "F_DP: %1 communication, connection %2 reports a system error %3 (%4)".
System variable: Substitute value signal, $A_FSDP_SUBS_ON
System variable $A_FSDP_SUBS_ON[1...n] is used to signal that F_RECVDP has output
substitute values to the application.
The system variable $A_FSDP_SUBS_ON is cyclically compared with the corresponding PLC
variables FSDP[1...3].SUBS_ON. If unequal, there is a system error and this is displayed using
Alarm 27355 "F_DP: %1 communication, connection %2 reports a system error %3 (%4)".
System variable: diagnostics data, $A_FSDP_DIAG
System variable $A_FSDP_DIAG[1...n] is used to signal the cause of the communication error
determined by F_SENDDP.
The system variable $A_FSDP_DIAG is
variables FSDP[1...16].DIAG.
Safety Integrated
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
8.4 Safety-related CPU-CPU communication (F_DP communication)
not cyclically compared with the corresponding PLC
Connecting sensors and actuators
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