Siemens Sinumerik 840D sl Function Manual page 289

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If a difference is detected between the signals of both channels, this is indicated
using Alarm 27090/27091 and the configured stop response (STOP D/E) is initia-
ted if the SPL commissioning phase has been defined to have been completed.
If the user attempts to acknowledge the initiated alarms and stop responses,
without having resolved the cause of the CDC error, then the stop response as well
as the alarm are initiated again.
To acknowledge a fault in the SPL--CDC, then the signal channel 1 reset
(DB21.DBX7.7) must be set for at least 100 ms.
For PLC--controlled axis the axis--specific reset must first be set up via
DB3x.DBX28.1 with a negative edge of the channel 1 reset.
The criterion "commissioning phase completed" is derived from the NCK--MD
$MN_PREVENT_SYNACT_LOCK[0,1] in the NCK. If one of the two field entries is
not equal to 0, "commissioning phase completed" is set by CDC internally. On the
PLC side, this criterion is entered using DB18.DBX36.0. If this bit is set to "1", then
the commissioning phase is considered to have been completed. An SPL--CDC
error results in a stop response only after the SPL commissioning phase has been
completed.
The stop response for an SPL--CDC error is set in the NCK using NCK--MD
$MN_SPL_STOP_MODE. If the MD value is 3, for an SPL--CDC error, a STOP D
is initiated -- for an MD value of 4, a STOP E is initiated. On the PLC side, this stop
response is entered using DB18.DBX36.1. If this bit is set to "1", for an SPL--CDC
error, a STOP E is initiated -- otherwise a STOP D.
Any changes to data on the NCK and PLC side do not take effect until after power
on.
Clearing the external SPL outputs for SPL system errors
If communication between NCK and PLC is interrupted with reference to the SPL--
CDC, then all external SPL output signals ($A_OUTSE/$A_OUTSEP) are cleared
with a 5 s delay.
This state occurs if data for crosswise data comparison is not exchanged between
the NCK and PLC for one second. This is due to the fact that
-- the one second limit of the user cycle limit in the PLC (OB1 cycle) was
exceeded.
-- a system error has occurred. The NCK or PLC system software no longer runs
due to a system error -- therefore interrupting communications.
Behavior of the NCK
The specified timer of 5 s is started if Alarm 27092 "Communication interrupted for
crosswise data comparison NCK--SPL, error detected by %1" is initiated. This is
independent of which component (NCK or PLC) interrupted the alarm.
The system variable $A_STATSID, bit 29 = 1 is used to indicate to the SPL user
that this timer has been started. This means that he has a possibility of initiating
plant/system--specific actions before the system deletes (clears) the output.
© Siemens AG 2015 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
Connecting Sensors/Actuators
7.5 Safe programmable logic (SPL)
7-289