Siemens CPU 948 User Manual

4.3.7
Extended AUTOMATIC
WARM RESTART with the
CPU 948 (HOT RESTART)
The "HOT RESTART" mode specified in the IEC 1131 standard, part
1 is also possible in the CPU 948. The "HOT RESTART" is a warm
restart controlled by a battery-backed clock (according to IEC 1131).
The clock monitors the time between switching off and switching on
the power supply for the CPU. Whether or not a warm restart is then
permitted depends on the time elapsed.
The automatic "HOT RESTART" of the CPU 948 is not supported
directly by the system program, which means that you must program
this yourself.
The basic functions available are the AUTOMATIC WARM
RESTART (OB 22) and the real time clock which although internal is
backed up by an external battery.
A "HOT RESTART" is programmed as shown below:
Mode Activity/block
RUN Save time (time of day and date) regularly from the external clock in defined memory
cells (e.g. in data words):
- at the end of the cycle in OB 1
or
- time-controlled by timed interrupts (e.g. OB 10), if higher accuracy is necessary
AUTO-
MATIC
WARM
RESTART
OB 22
Calculate down time:
T
down
= first time value after return of power - last time value saved before power failure
IF ... THEN...
Down time > default maximum value Stop warm restart
(STP operation)
or
execute modified warm restart
Down time ≤ default maximum value
Continue warm restart
START-UP Mode
CPU 948 Programming Guide
C79000-G8576-C848-04
4 - 27

Siemens CPU 948 Specifications

General

Brand	Siemens
Model	CPU 948
Category	Controller
Language	English