Siemens Sinumerik 840D sl Function Manual page 290

Connecting Sensors/Actuators
7.5 Safe programmable logic (SPL)
After this time has expired, the system deletes the external SPL outputs. The
status variable $A_STATSID, bit 29 remains set. When reading--back the external
outputs in the NCK--SPL via the system variable $A_OUTSE, "0" is read corre-
sponding to the actual output status.
Behavior of the PLC
If, on the PLC side, it is detected that the communication timeout has been
exceeded, then a timer is started with 5 s.
After this time has expired, the PLC goes into Stop (by calling an SFC46). This
state can only be exited using a power on.
After the 5 s timer has expired, for diagnostics purposes, the PLC outputs Alarm
400253 "PLC--STOP due to SPL system error". At the same time, an entry with the
same significance is located in the diagnostics buffer.
Using the status signal DB18.DBX119.5, the SPL programmer and the NCK is
provided with the information that the timer was started. This means that he has
the possibility of initiating system--specific actions before the PLC goes into the
stop condition.
Note
In order to achieve the shortest possible response time, the system variable
$A_STATSID, bit 29 and the status signal DB18.DBX119.5 must be evaluated in
the SPL in order to bring, as far as possible, the SPL--SGA into a safe state
(cleared SPL--SGA).
Boundary conditions
The user must take into consideration the following points regarding the functioning
of the crosswise data comparison:
S Both channels (NCK/PLC) must execute the same logic.
S Do not implement any response sequences or sequence controllers that are
externally controlled using short input pulses. This is because short pulses of
this type may only be sent and processed in one channel because of sampling
effects.
S Unused inputs/outputs/markers of the SPL must be assigned the default value
= 0; single--channel use of individual bits for non--safety relevant purposes is
not permissible.
S External STOPs must be enabled (they are also used internally) and can be
extracted from the SPL if required. When using the SPL via MD
$MA_SAFE_EXT_STOP_INPUT[0], for all safety axes, the external STOP A
must be parameterized at the SPL interface. If this condition is not fulfilled, then
Alarm 27033 is output.
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SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
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10/15