Siemens SINUMERIK 840D sl Function Manual page 183

03.06
Note
The OB40 run time increases by the following time for each F module.
S CPU 317-2 DP: approx. 0.25 ms
In order to reduce the possible resulting computational load, machine data:
S MD 10098: $MN_PROFISAFE_IPO_TIME_RATIO
(factor, PROFIsafe communications clock cycle)
can be used to modify the ratio between the PROFIsafe and interpolation clock
cycle.
In order to achieve a sufficiently fast response time regarding PROFIsafe-commu-
nications, the PROFIsafe clock cycle may not be parameterized greater than
25 ms. The selected PROFIsafe clock cycle is displayed in the machine data:
S MD 10099: $MN_INFO_PROFISAFE_CYCLE_TIME
(PROFIsafe, communications clock cycle)
For a PROFIsafe clock cycle of greater than 25 ms, when the control boots the
next time, an alarm is displayed:
S Interrupt: 27200 "PROFIsafe cycle time %1 [ms] is too long"
PROFIsafe clock cycle and DP cycle time
The PROFIsafe clock cycle should be parameterized longer than the DP clock cy-
cle time displayed by STEP 7: HW Config. Otherwise, the load (in time) on the
PLC user program is increased as a result of unnecessary OB40 interrupts.
Note
The PROFIsafe clock cycle should be parameterized so that the following applies:
12 ms < PROFIsafe clock cycle < 25 ms
PROFIsafe clock cycle overruns
Even if the parameterized software operates error-free in normal operation, run
time fluctuations in the PLC operating system (e.g. processing diagnostic alarms)
can mean that the processing of the OB40 interrupt was not able to be completed
before the start of the next PROFIsafe clock cycle.
In this particular case, the NCK attempts, up to a limit of 50 ms after the last cor-
rectly processed PROFIsafe clock cycle, to initiate an OB40 interrupt. The re-
peated attempts to initiate the OB40 interrupt are no longer executed in the PRO-
FIsafe clock cycle but in the IPO clock cycle.
After this 50 ms limit value is exceeded,
S Interrupt: 27253 "PROFIsafe communications error F master components %1,
error %2"
is displayed and the configured Stop response (Stop D or E) is output to the safety
axes.
© Siemens AG, 2006. All rights reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 03.2006 Edition
Connecting Sensors/Actuators
7.2 Connecting I/O via PROFIsafe
7-183