Operating modes describe the states of the CPU. The following operating modes are possible: ● STARTUP ● RUN ● STOP ● HOLD In these operating modes, the CPU can communicate via the PN/IE interface, for example.
If the CPU is not ready for operation, it is in one of following two operating modes: ● Off-voltage, in other words, line power is switched off. ● Defective, which means that an internal error has occurred.
Operating mode transitions
① POWER ON → STARTUP
After switching on, the CPU goes to "STARTUP" mode if "Warm restart" startup type is set, and the hardware configuration and the program blocks are consistent. Non-retentive memory is cleared and the contents of non-retentive DBs are reset to the initial values of the load memory. Retentive memory and retentive DB contents are retained.
② POWER ON → STOP
When startup type "No startup" is set, the CPU goes to "STOP" mode after the supply voltage is switched on. Non-retentive memory is cleared and the contents of non-retentive DBs are reset to the initial values of the load memory. Retentive memory and retentive DB contents are retained.
③ STOP → STARTUP
The CPU switches to "STARTUP" mode if CPU is set to "RUN" from the programming device, and the hardware configuration and the program blocks are consistent.
④ STARTUP → STOP
The CPU returns to the "STOP" mode in the following situations: ● Error detected during startup. ● The CPU is set to "STOP" from the programming device. ● A STOP command is processed in the STARTUP OB.
⑤ STARTUP → RUN
If the STARTUP is successful, the CPU switches to "RUN".
⑥ RUN → STOP
The CPU returns to the "STOP" mode in the following situations: ● An error is detected that prevents continued processing. ● The CPU is set to "STOP" from the programming device. ● A STOP command is processed in the user program.
⑦ STARTUP → HOLD
Breakpoint in the start-up routine reached.
⑧ HOLD → STARTUP
Breakpoint in the start-up routine exited by setting to "RUN" from the programming device.
⑨ RUN → HOLD
Breakpoint reached.
⑩ HOLD → RUN
Breakpoint exited by setting to "RUN" from the programming device.
⑪ HOLD → STOP
Operation switch/display or setting the programming device to "STOP".
After turning on the CPU, it executes a startup program before starting to execute the cyclic user program. By suitably programming startup OBs, you can specify certain initialization variables for your cyclic program in the startup program.
There is no rule in terms of the number of startup OBs. That is, you can set up one or several startup OBs in your program or none at all.
Parameter settings for startup characteristics
You can specify whether the CPU remains in "STOP" mode or whether a warm restart is performed. You can also set the response during startup ("RUN" or previous mode) in the "Startup" group of the CPU properties.
to be continued...
In "RUN" mode, the cyclic, time-driven and interrupt-driven program sections execute.
Addresses that are in the "Automatic Update" process image are automatically updated in each program cycle. ● The process image output is read out. ● The process image input table is read. ● The user program is executed.
Active data exchange between S7-1200 CPUs by means of Open User Communication is only possible in "RUN" mode.
In "STOP" mode, the user program is not executed.
All outputs are disabled or react according to the parameter settings: They provide a substitute value as set in the parameters or retain the last value output and bring the controlled process to a safe status.
The "HOLD" operating mode is reached through a breakpoint in a block that you are testing in single step mode. The single step mode test function is available in the STL and SCL programming languages.
In "HOLD" operating mode, events are not initiated and the user program is not executed.
All outputs are disabled or react according to the parameter settings: Outputs supply a configured substitute value or keep the last value output and bring the controlled process to a safe operating state.
Timers and watchdogs are stopped. The timers for time-driven events are stopped.
In HOLD operating state, hardware interrupt OBs are not started by external interrupt triggers(e.g. hardware interrupt input).
