hello zafarltc;
First, When you need to ask a new question, start a new post, please; inserting you request in an ongoing discussion will help neither you nor the other participants.
You seem confused about many basic S7 programming issues. I can start by suggesting the following site, where you will find tutorials on S7-300 programming issues; Section B4, for example, is dedicated to Data Blocks:
http://www.automation.siemens.com/fea/html_76/down_module.htm
To give you a quick answer on your first question:
whats is a DB And In side DB How Many Words And Byte And Bits
Data memory in a S7 PLC is of 2 kinds: defined (input table [Ix.x], ouput table [Qx.x] and flag table [Mx.x]) and undefined: what can be accessed in Data Blocks.
A data block is a structure defined by the user (you, in this case) to group registers required for a specific function. If you want to control a motor, for example, you might need:
-a Start bit
-a Stop bit
-an alarm bit
-an overload bit
-a motor speed feedback signal
-a bearing temperature register
In S7 philosophy, you would create a DB for this in this way:
The absolute name (address) of the DB is DB1, and the offset address of each element of the structure is shown in the left-hand column.
So you can use absolute addressing of the Overload and Alarm bits in DB1 this way:
Or you can assign a Symbol (TEST_MOTOR) to DB1, and use symbolic addressing of the same Overload and Alarm bits this way:
Hope this helps,
Daniel Chartier
