Structure Of The Clock Data Area - Siemens SIMATIC S5-100U System Manual

The Integral Real-Time Clock
12.4

Structure of the Clock Data Area

You need only to change the default values in DB1 to program the clock in DB1. See section 12.2.
During start-up, the DB1 interpreter writes all information into the system data area.
TIP: Do not attempt to set parameters in the system data, or to access directly from the user
program unless you have extensive knowledge of the system.
You must store the location of the clock data area in system data 8 and 9.
Data exchange between DB1 or the control program and the integral real-time clock is always
through the clock data area.
• 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).
• DB1 and the control program store the settings for prompt times and operating hours counters in
the same data area.
The control program can only read from or write to the clock data area. The control program can
never access the clock directly. Figure 12-6 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 settings
Figure 12-6. How DB1 or the Control Program and the Clock Access the Clock Data Area
12-8
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 6120-02b
S5-100U