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Objectives
- Know The Elementary & Complex DB.
- How To Create DB.
- Familiar With Addressing & Accessing Data Element.
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Data Blocks (DBs)
Function
FC10
Function
FC20
Function
block
FB1
OB1
Global data
DB20
Accessible to all blocks
Instance data
DB5
Instance DB for FB1
Elementary data types (up to 32 bits)
• Bit data types (BOOL, BYTE, WORD,
DWORD, CHAR)
• Mathematical data types (INT, DINT,
REAL)
Complex data types (longer than 32
bits)
• Time (DATE_AND_TIME)
• Array (ARRAY)
• Structure (STRUCT)
• Character chain (STRING)
User-defined data types (longer than 32
bits)
Data type UDT (User Defined Type)
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Entering, Saving, Downloading and Monitoring a Data Block
Declaration
View
Data View
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Addressing Data Elements
The number of data blocks
available depends on the CPU
you use.
The maximum block length is
8-KByte for the S7-300 and 64-
KByte for the
S7-400.
07
8 Bits
Data Byte 0 DBB 0
Data Byte 1 DBW 0
Data Byte 8191
DBD 8188
DBW 8190
DBB 8191
Data Byte 2
DBD 0
Data Byte 3
DBX 4.1
Accessing Data Elements
OPN DB 9
A DBX 0.0
OPN DB 9
L DBB 1
OPN "Values"
T DBW 2
A DB9.DBX0.0
L DB9.DBB1
L DB9.DBW2
OR
OR
OR
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Exercise:
1- In FC6, Write a PLC program, using DB6 to calculate the following equation:
K = 4X + 18XZ + 2Z/2 + 2(2Y+3)
Then find the value of K at: X=2, Y=1 and Z=2
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Answer of Exercise 1:
IN The DB:
The value of K at: X=2, Y=1 and Z=2
K=91
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Editor's Notes
Shared DB
Shared data blocks are used to store global data. That is, for storing general data that can be accessed by every logic block (OB, FC, FB).
Instance DB
Instance data blocks are used as the "private memory area" or as the "memory" for a function block (FB). The parameters and the static variables of an FB are managed in its instance DB.
Declaration View
Data blocks are edited in the "declaration view", that is, the user declares the variables needed for storing the data here. The variables are created in a table, organized in lines and columns.
Save
You save the data block on the hard disk of the programming device using the "Diskette" icon.
Download
You have to download data blocks to the CPU, just as you do with logic blocks.
Data View
You can monitor online the current variable values in the data block (values of the variables in the CPU). To do so, you must first go into the "View" menu and switch to the "Data View". You can then activate the function using the "Glasses" icon.
Initialize DB
When you initialize a data block you overwrite the variable‘s current values with the initial values. This is also necessary when initial values that have been changed later on have to be accepted as actual values.View -> Data View -> Edit -> Initialize Data Block
