DB size

Hello everybody,
I have got a DB(data block) in which I am saving data of a UDT(50 byte) type in an array, in every cycle carried out on the machine (about 100 cycles per day). This DB created temporarily to save data for tracking down a problem on the machine.
here is my questions:
1.what is the maximum size of the DB(how big my array can be)?(CPU 315-2dp)
2.what will happen when amount of data passed this size?
3.how can I read and save these actual values of the DB and copy it in text format?
4.after reading these values how can I reset actual values back to initial values so I can have a fresh DB for saving new cycles?

it's better to use a software called 'PLC-Analyzer' to tracking down your problem.

hill831017 said:

it's better to use a software called 'PLC-Analyzer' to tracking down your problem.

Click to expand...

Not what he asked for, nor necessarily useful in this case. The problem may be the process, not the program (in fact it usually is).

To the OP:

1. I think it's 16kB off the top of my head, which should be ample. You might need to read the processor manual for more detail. From memory the pointer data format is 16 bit, so it might also be 64kB...
2. Nothing, unless you make a mistake with the pointer used to write to it or something.
3. You can copy and paste the DB from the "online" view into an offline project, then open it in the DB editor when the test is done. The values you see should be up to date, and you can copy and paste into Excel for processing.
4. Copy and paste the blank initial DB in your offline project into your offline version - this will overwrite any accumulated values.

You should use a plc datalogger with triggermode. For S7 you can get a demo here.

1. For the latest version 315-2DP (6ES7315-2AH14-0AB0) max DB size is 64 kB.

2. Depends on your code. If it tries to access memory outside the DB, it may trigger OB121.

Why are people trying to sell the OP software?

1. Answered by Jesper.

2. Not sure what will happen exactly, I would presume you would be indirectly accessing the data areas, best case would be it would not let you write, worse case you would corrupt the code, best to put in limit management in the code.

3. You would need an OPC server to move the data into a PC program, such as excel (easiest way).

I've actually done the same recently but had no OPC, so I go online, transfer the online DB to the offline DB, then create a source of the DB. I then open the source and copy and paste the data into an excel sheet. The data is not really reader friendly, so I created a small VBA program that puts the data into columns and converts to readable data.

4. You can use SFC4 (FILL) to move a zero byte into all bytes in the DB.

Binaural said:

Not what he asked for, nor necessarily useful in this case. The problem may be the process, not the program (in fact it usually is).

To the OP:

1. I think it's 16kB off the top of my head, which should be ample. You might need to read the processor manual for more detail. From memory the pointer data format is 16 bit, so it might also be 64kB...
2. Nothing, unless you make a mistake with the pointer used to write to it or something.
3. You can copy and paste the DB from the "online" view into an offline project, then open it in the DB editor when the test is done. The values you see should be up to date, and you can copy and paste into Excel for processing.
4. Copy and paste the blank initial DB in your offline project into your offline version - this will overwrite any accumulated values.

Click to expand...

Number 4 should read "copy and paste the blank initial DB in your offline project into your ONLINE version - this will overwrite any accumulated values". Sorry! If you want to do this programatically, then SFC4 will do the job as per PeterW's comment.

PeterW - I think I made that mistake of trying to write data to a DB with an out-of-range pointer once before, and the result was not program corruption but an error.