Siemens SIMATIC S7 Operating Instructions

SIEMENS AG PRODAVE S7
Toolbox for Data Link PGs/PCs to SIMATIC S7
11
- Prior to starting the PRODAVE application under MS-DOS it is required to
activate the drivers for the used interface.
3.4 Differences between S5 and S7
The main difference between S5-PLCs and S7-PLCs is the management of
data blocks. S5 data blocks are processed word by word, whereas the S7 data
blocks are processed byte by byte.
S5 S7
bit 15 .. bit 0 bit 7..0 bit 7..0
= DW 0
= DW 2
= DW 4
= DW 6
...
When using the d_field_read function, the data block is accessed byte by byte
such as, for instance, applies to the flag area.
When you read 3 data words using the db_read function, the PLC transfers
DBW0 - DBW5. I.e. three 16bit words are available for processing in the
PG/PC, which the PLC addresses via DBW0, DBW2 and DBW4, by the
PG/PC, however, they are addressed via DW0, DW1 and DW2.
DB0 DB1
DB2 DB3
DB4 DB5
DB6 DB7
... ...
DW 0
DW 1
DW 2
DW 3
...

Siemens SIMATIC S7 Specifications

General

Brand	Siemens
Model	SIMATIC S7
Category	Controller
Language	English