13.2 Structure Of The Clock Data Area - Siemens SIMATIC S5-90U System Manual

Integral Real-Time Clock

13.2 Structure of the Clock Data Area

You need only to change the default values in DB1 to program the clock in DB1. See section 13.5.
During start-up, the DB1 interpreter writes all information into the system data area (for system data
assignment through integral clock see Appendix B).
Data exchange between DB1 and the integral real-time clock is always through the clock data area.
On the one hand, the integral real-time clock stores current time, date, and operating hours counter
values in the clock data area (flag area, data block, input area, or output area). On the other hand,
DB1 stores the settings for prompt times and operating hours counters in the same data area.
The control program can read or write only the clock data area. The control program can never
access the clock directly. Figure 13-1 illustrates the relationship between DB1 or the control
program, the clock data area, and the integral real-time clock.
DB1/
Control
program
Reading clock data
Transferring manipulated
variables
Figure 13-1. How DB1 or the Control Program and the Clock Access the Clock Data Area
Note
The time in the clock data area is updated each time after 1 s at the beginning of the
next program cycle (at the cycle checkpoint). Reading clock data in OB 22 leads to
faulty values.
13-2
Clock data area
Current clock
time/date
(words 0 to 3)
Settings
clock time/date
(words 4 to 7)
Prompt time
(words 8 to 11)
Current operating
hours count
(words 12 to 14)
Settings operating
hours counter
(words 15 to 17)
Clock time/date of
the last switch from
RUN to STOP
(words 18 to 21)
Integral real-
time clock
The clock writes clock data
in the clock data area
The clock accepts the settings
from the clock data area
EWA 4NEB 812 6115-02b
S5-90U/S5-95U