Siemens SINUMERIK 840Di Function Manual page 1234

Detailed Description
2.7 Structure and functions of the basic program
2.7.3 Time-interrupt processing (OB 35)
General
The user must program OB 35 for time-interrupt processing. The default time base setting of
OB 35 is 100 ms. A different time base can be selected using the STEP7 "HW Config" tools.
However, the OB 35 time setting must be at least 3 ms in order to avoid a PLC CPU stop.
The stop is caused by reading of the HMI system state list during power-up of the HMI. This
reading process blocks priority class control for approx. 2 ms. The OB 35 with a time base
set to a rather lower value is then no longer processed correctly.
2.7.4 Process-interrupt processing (OB 40)
General
A process interrupt OB 40 (interrupt) can, for example, be triggered by appropriately
configured I/Os or by certain NC functions. Due to the different origin of the interrupt, the
PLC user program must first interpret the cause of the interrupt in OB 40. The cause of the
interrupt is contained in the local data of OB 40.
(For more information please also refer to the SIMATIC STEP7 description or the STEP7
online help).
2.7.5 Diagnostic interrupt, module failure processing (OB 82, OB 86)
General
A module diagnosis or module failure on an I/O module triggers OB 82 / OB 86. These
blocks are supplied by the basic program. The basic program block FC5 is called in these
OBs. This is wired by default to trigger a PLC stop in the event of an error being detected. If
the cause of the error is removed, a PLC stop will not be triggered. A PLC stop does not
occur on the PROFIBUS MCPs indicated in the FB1 parameters. The response can be
changed by modifying the FC5 parameter setting.
2-40
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0