Technical data

You can do the following in the RESTART OBs:
•• set flags,
•• start timers (the start is delayed by the system program until the
user program enters the RUN mode),
•• prepare the data traffic of the CPU with the I/O modules,
•• execute synchronization of the CPs.
OB 20 COLD RESTART:
When the CPU executes a MANUAL or AUTOMATIC COLD
RESTART, the system program calls OB 20 once. In OB 20, you can
store a STEP 5 program that executes preparatory steps for restarting
cyclic program execution:
After OB 20 is processed, the cyclic program execution begins by
calling OB 1 or FB 0.
If OB 20 is not loaded, the CPU begins cyclic program execution
immediately after the end of a COLD RESTART (following the
system activities).
OB 21 MANUAL WARM RESTART or RETENTIVE MANUAL
COLD RESTART:
When the CPU carries out a MANUAL WARM RESTART or
RETENTIVE MANUAL COLD RESTART, the system program calls
OB 21 once. In OB 21, you can store a STEP 5 program that carries
out specific activities once before cyclic program execution is
resumed.
MANUAL WARM
RESTART
After OB 21 is processed, for MANUAL WARM RESTART the
cyclic program execution continues with the next statement after the
point at which it was interrupted. The following conditions apply:
•• The disable command output signal (BASP) remains active while
the rest of the cycle is processed. It is only cleared at the beginning
of the next (complete) cycle.
•• The process output image is reset at the end of the remaining cycle.
If OB 21 is not loaded, then at the end of a MANUAL WARM
RESTART and after performing system activities the CPU begins
program execution again at the point at which the program was
interrupted.
4
RESTART Mode
CPU 928B Programming Guide
C79000-B8576-C898-01
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