Siemens SINUMERIK 840D sl Function Manual page 209

05.08
If the value entered does not match the value displayed in the F modules, an alarm
is issued when the control boots:
S Alarm: 27220 "PROFIsafe: Number of NCK F modules (%1) < > Number of S7
F modules (%2)"
In this case, alarm parameter %2 contains the value 0.
PROFIsafe clock cycle
The PROFIsafe clock cycle defines the time grid in which new F telegrams are
generated by the F master for transfer to the F modules. The PROFIsafe clock
cycle is derived as standard from the interpolation cycle in the ratio 1:1.
As part of the PROFIsafe communications, a cyclic interrupt of the PLC user pro-
gram (OB1) is made. This is realized in the PROFIsafe clock cycle via OB40.
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 Alarm: 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 cycle 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
© Siemens AG 2008 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 05.2008 Edition
Connecting Sensors/Actuators
7.2 Connecting I/O via PROFIsafe
7-209