Backup Of The Hardware Clock - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
• The operating system resets the "transfer settings" bits (bits 2, 10, and 14 in the status word)
under the following conditions.
- The settings have been transferred.
- The settings have not been transferred because they were outside of the permissible range.
The corresponding error bit (bits 0, 8, and 12 in the status word) is set.
• The operating system does not reset the "transfer settings" bits (bits 2, 10, and 14 in the status
word) under the following conditions.
- The system data for the clock is either incorrect or not available.
- The clock data area is too small.
- The clock is defective (hardware error).
Scanning the Status Word
In a data block, you can use the "P <data word number> <bit number>" operation to scan the
individual bits of a data word. In the flag area, you can scan the individual bits if you enter the
<byte address> and the <bit number>.
Example: The status word is stored in DW13. You are checking to see if the set prompting time
has been reached.
The "P D 13.13" instruction triggers a scan.
If the status word is stored in FW12, then the same scan would be "A F 12.5".
13.4

Backup of the Hardware Clock

If there is a backup battery, the clock continues to run even after Power OFF. If the programmable
controller does not have a backup battery, the clock values will be set at "October 1, 1991, 12.00.00
o'clock, weekday: 3" when the clock is initialized after a Power ON. The default is the 24-hour time
mode. You should install a battery only during Power ON; otherwise, you would lose the clock data.
EWA 4NEB 812 6115-02b
Integral Real-Time Clock
13-7