P3: Basic PLC Program for SINUMERIK 840D sl
13.8 Structure and functions of the basic program
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
879
M decoder
M functions can be used to transfer both switching commands and fixed point values. Decoded dynamic signals
are output to the CHANNEL DB interface for standard M functions (range M00 - M99) signal length = 1 cycle
time).
G group decoders
In the case of G functions sent by the NCK, the related groups are decoded and the current G number is entered
in the corresponding interface byte of the CHANNEL DB, i.e. all active G functions are entered in the channel
DBs. The entered G functions are retained even after the NC program has terminated or aborted.
M, S, F distributor
The M, S, F, distributor is used to enter spindlespecific M words M(1...6)=[3,4,5], S words and F words for axial
feeds in the appropriate spindle and axis data blocks. The criterion for distribution is the extended address, which
is passed to the PLC for M words, S words and axial F words.
MCP signal transmission
On the SINUMERIK 840 D, depending on the bus connection, MCP signals are transmitted to the parameterized
I/O areas either directly to the PLC or indirectly via an internal procedure using the basic program.
User messages
The acquisition and processing of the user error and operational messages is performed by an FC in the basic
program.
13.8.3 Time-interrupt processing (OB 35)
The user must program OB 35 for time-alarm 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 powerup 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.
13.8.4 Process interrupt processing (OB 40)
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.
References:
SIMATIC STEP 7 Description or Online Help of STEP 7
Note
During system startup, all G group bytes are initialized with the value "0".
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