Differences Between S5 And S7 - Siemens SIMATIC S7 Operating Instructions Manual

SIEMENS AG
- 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
bit 15 .. bit 0
DW 0
DW 1
DW 2
DW 3
...
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.
Toolbox for Data Link PGs/PCs to SIMATIC S7
S7
bit 7..0 bit 7..0
DB0 DB1
DB2 DB3
DB4 DB5
DB6 DB7
... ...
11
PRODAVE S7
= DW 0
= DW 2
= DW 4
= DW 6
...