Siemens S7 Start Process

Hi Everyone,

Newbie on step7, could anyone please explain in simple words the difference between COLD, WARM and HOT Restart? and what it actually does to the CPU? Also when you started writing program and download it to a CPU, would the program be automatically saved to MMC? I have seen my colleage working making mods on the program whilst online, would the changes made be saved on the MMC? By the way the unit we have is step7-300. Thanks.

Hi Franchois,

The load Memory On the s7-300 is stored On the mmc. When a program is downloaded from the programming device, it gets downloaded to the mmc. From there the necessary parts are copied to the work Memory (ram) where the program is processed.

A cold restart resets all values to their initially programmed values and starts the program from the beginning of the cycle.
Warm restart retains the retentive values from when the cpu was Last stopped and starts from the beginning of the program cycle with those memory and data block values.
Hot restart is only available on s7-400s and starts the program where it left off when the power went out or program was stopped.

If any of this is incorrect, someone feel free to correct me.

Thank you Jieve for clarification. Further to the question I previously asked about memory and starting up, we had a situation at work where one of our equipment equipped with step7-300 and touch panel via profibus would not work properly. It is a usual scenario where nothing is so serious and powering down and back on would resolve it straight away. This time several turning on and off did not get the machine running, to make long story short, what the engineer's done is CPU Memory Reset and the machine appeared to be ready and everything looks fine apart from the 5 recipes on the panel where all data resets to zero. They inputed all the parameters and machine run fine again. Could anyone help me answer my questions:

1. Where are those parameters stored and why they were wiped off during cpu reset but stays during production shutdown where there is no power to the machine?

2. If you entered data to touch panel, where are they stored?

3. How can we prevent it from happening again i.e. Doing memory reset would not erase the data on the panel?

My best guess is that the recipes were saved as retentive values in the CPU. On a power outage, they get copied to the mmc or backup Memory so they dont get deleted when the power goes out. A Memory reset deletes all data in the RAM (work Memory) and deletes all retentive Memory values and replaces them with the default initial values. The only way i can see fixing the problem would be to program the recipes as default values and redownload the program. However, if the recipes change and you do a reset, you'll still have to Update them again.

I should add that the difference between a cold and warm restart is that a memory reset is performed On a cold restart.

Hi Jieve, thanks a lot for all the infos, I will work my way up to find out considering those things you mentioned. Also a good way to aid me getting familiar with s7. Cheers.