Siemens SINUMERIK 840D sl Function Manual page 521

The user interface is set in all cases:
$A_FRDP_ERROR = 1
$A_FRDP_SUBS_ON = 1
$A_FRDP_DIAG corresponding to the detected communication error
SPL inputs $A_INSE corresponding to $A_FRDP_SUBS
Whether initiated as fault response STOP D or STOP E, can be parameterized using:
NCK: $MN_SAFE_SPL_STOP_MODE
PLC: DB18.DBX36.1
Default value: After the control boots, initially, the values saved in MD
$MN_SAFE_SDP_ERR_REAC become active.
System variable $A_FRDP_ERROR
The system variable is used to indicate that there is a communication error. The error cause
determined by F_RECVDP is contained in the diagnostics data $A_FRDP_DIAG.
0 = normal mode
1 = communication error
System variable $A_FRDP_SUBS_ON
The system variable is used to indicate that substitute values are output to the application.
0 = output of process values
1 = output of substitute values
System variable $A_FRDP_ACK_REQ
The system variable is used to signal that after a communication error, cyclic F-telegrams are
again cyclically exchanged error-free - and to acknowledge the error and to output the process
values, a user acknowledgment is still required via the interface signal DB18.FRDP_ACK_REI
or a channel_1 reset.
System variable $A_FRDP_DIAG
The system variable is used to indicate the cause of the communication error determined by
F_RECVDP.
Bits 0 - 3: Reserved
Bit 4: 1 = timeout detected
Bit 5: 1 = sequence number error detected
Bit 6: 1 = CRC error detected
Bit 7 - 12: Reserved
Bit 13: 1 = discrepancies in the F-telegram data (TelegramDiscrepancy)
Safety Integrated
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
Data descriptions
9.7 System variable
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