2.4 Data Blocks
Data blocks (DB) or extended data blocks (DX) are used to store the
fixed or variable data with which the user program works. No STEP 5
operations are processed in data blocks.
The data of a data block includes the following:
•• various bit patterns (e.g. for status of a controlled process)
•• numbers (hexadecimal, binary, decimal) for timer values or arith-
metic results
•• alphanumeric characters, e.g. for message texts.
Structure of a data block
A data block (DB/DX) consists of the following parts:
•• block preheader (DV, DXV),
•• block header
•• block body.
Block preheader
The block preheader is created automatically on the hard or floppy
disk of the PG and not transferred to the CPU. It contains the data
formats of the data words entered in the block body. You have no
influence over the creation of the block preheader.
Note
When you transfer a data block from the PLC to diskette or hard
disk, the corresponding block preheader can be deleted. For this
reason, you must never modify a data block with different data
formats in the PLC and then transfer it back to diskette, otherwise
all the data words in the DB are automatically assigned the data
format you selected in the presets screen form.
Data Blocks
CPU 948 Programming Guide
C79000-G8576-C848-04
2 - 35
To Next Page
Loading...
Need help?
General
