Technical data

Appendix
27.8 Setting the Operating Behavior
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 683
In STOP mode, the runtime meter is stopped. Its count value is retained even after a memory
reset. During a restart (warm restart), the runtime meter must be restarted by the user program;
during a hot restart, it continues automatically if it had already been started.
You can set the runtime meter to an initial value using SFC2 SET_RTM. You can start or stop the
runtime meter with SFC3 CTRL_RTM. You can read the current total operating hours and the state
of the counter ("stopped" or "counting") with SFC4 READ_RTM.
A CPU can have up to eight run-time meters. Numbering starts at 0.
27.8.4 Using Clock Memory and Timers
Clock Memory
The clock memory is a memory byte that changes its binary state periodically at a pulse-pause
ratio of 1:1. You select which memory byte is used on the CPU when you assign parameters for the
clock memory using STEP 7.
Uses
You can use clock memory bytes in the user program, for example, to activate flashing lights or to
trigger periodic activities (for example, measuring an actual value).
Possible Frequencies
Each bit of the clock memory byte is assigned a frequency. The following table shows the
assignment:
Bit of the Clock Memory
Byte
7 6 5 4 3 2 1 0
Period Duration (s) 2.0 1.6 1.0 0.8 0.5 0.4 0.2 0.1
Frequency (Hz) 0.5 0.625 1 1.25 2 2.5 5 10
Note
Clock memory bytes are not synchronous with the CPU cycle, in other words, in long cycles, the state of the clock
memory byte may change several times.
Timers
Timers are a memory area of the system memory. You specify the function of a timer in the user
program (for example, on-delay timer). The number of timers available depends on the CPU.