one more interesting problem

Hi friends
I am facing one strange problem these days.I have siemens S7 PLC communication and WinCC in our system.In PLC we are using DB121 for communicating with WinCC.
The codes in PLC (example)
A db121.dbx1.0( from WinCC button)
s db121.dbx5.0
When i click from HMI and set db121.dbx5.0 everything is ok.The system working normal.
But problem comes when i download db121 to plc without doing anything , db121.dbx5.0 is getting reset.
for checking purpose i changed the code as
A m1.1(permanent 1 bit)
s db121.dbx5.0
and download db121 to plc , db121.dbx5.0 doesnot reset.

Your WinCC button is acting like a wired push button


You press the push button and DB121.DBX5.0 will be set. You let go and it stays set. You download DB121 and DB121.DBX5.0 will now be whatever is in the offline copy of DB121 (false in your case).

You could use a retained M flag (see h/w config for range of M flags that are retained);


You will also need to code the reset of the M flag where you currently reset DB121.DBX5.0

???

Hi LD
It seems you have not understood my problem.If something is set in PLC and running perfectly.How can it reset only when you download DB 121 withoud changing any thing.
Right now my system is working ok and if i open step7 and without doing anything i download DB121 to plc,it reset the bit.

When you download DBs to Siemens PLC they will always be set in inital state.

Copy datas to memory or maybe easy to VAT-table, then download, and then copy back into DB.

There are also another way, I dont remember it.

Dut why do you need to download DB all the time? This is strange.

Open the data block and put the glasses on to go online. Look at the online value of db121.dbx5.0. Now click the glasses to go offline.

Do View - Data view. Now look at the offline value of db121.dbx5.0.

When you download DB121 the plc will have the value of the offline data view.

Here is how to get the online data to your offline copy:
1. Make a backup of your Step 7 project in case anything goes wrong.
2. Right-click blocks folder and do compare blocks...
3. Set to date timestamp only
4. When compare blocks says no problem with DB, go on.
5. In Simatic Manager open an online view of your project. This is a toolbar button you click.
6. In online window of blocks, drag and drop your DB from online to offline. This copies the online DB to your offline project. Now you have the data values.
7. Make your change to the DB and download.

Please note that data values that change in the time it takes you to download will of course be overwritten with the values you had offline.

hioben said:

When you download DBs to Siemens PLC they will always be set in inital state.

Click to expand...

Only set at initial state when first downloaded. Once the DB exists in the PLC the values will be set to the offline value. To see the offline value do View - Data View. You can modify the data separate from the initial value.

????

Thanks gents
Hioben , we found this problem when one day we added something in DB and when we downloaded it.Then we normalised the DB back to original.But still the problem was same.
It seems someone did something somedays back which created this problem.Because of it , we were not able to modify anything when the system was running as it will trip the plant.So we used to modify the things in plant shutdown.
Now I did same as Paul suggested , i mean copy the DB from online to offline during plant stoppage.It is ok now ,i mean i am not facing that problem now.Let me check when we start our plant.
Thanks again to all you guys.