Siemens SIMATIC S5-100U, System Manual

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The Integral Real-Time Clock S5-100U
12.5 Structure of the Status Word and How to Scan it
You can scan the status word to identify errors in the entered settings. You can deliberately change
certain bits in the status word to enable or disable transfer or read operations. You can use
designated flag bits to govern the clock’s behavior when the programmable controller is switched
from the RUN to the STOP mode or during Power OFF.
• The status word can be located in the flag area or in a data block. You must define the location
of the status word in DB1 or directly in system data 9 and 10. See section 12.6.
• The integral real-time clock runs independently of the set operating mode. Access to the clock
data area depends on the set operating mode and the signal states of bits 4 and 5 in the status
word. You can set or reset these bits using the “S” or “R” operations in the control program.
- If you use an operator panel, such as the OP 396, to monitor the program, it is an
advantage to have the programmable controller update the clock time (the current date)
even in the STOP mode.
• 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 bits (bits 0, 8, and 12 in the status word) are 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).
• There are four types of bits in the status word.
- Clock flags
- Operating system flags
- Operating hours counter flags
- Prompt time flags
12-12
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