Siemens 6DD1607-0AA2 - Data Transfer Via I;O Accesses

Configuring
Application Module FM 458-1 DP - User Manual 4-9
A5E01078222-02 Edition 03.2009
4.3.3 Data transfer via I/O accesses
To transfer low data quantities: up to max. 128 bytes
Appropriate function blocks are available for each data transfer direction
and for each data type to be transferred.
SIMATIC-CPU FM 458-1 DP
Data type Transfer
command
(SL program)
Write
direction
CFC function
block
Data type
BYTE T PAB abs.addr. 
S7RD_B
BOOL
INT T PAW abs.addr.
S7RD_I
INT
DINT T PAD abs.addr.
S7RD_D
DINT
REAL T PAD abs.addr.
S7RD
REAL
BYTE L PEB abs.addr. 
S7WR_B
BOOL
INT L PEW abs.addr.
S7WR_I
INT
DINT L PED abs.addr.
S7WR_D
DINT
REAL L PED abs.addr.
S7WR
REAL
Table 4-2 Data types and the associated commands/blocks for peripheral accesses
The 8-bit CFC data type “BOOL“ is represented in the SIMATIC S7-CPU
as “BYTE“ data type. This means that the SIMATIC S7 user must
appropriately set or evaluate the decisive MSB (Most Significant Bit):
 S7-CPU: bit variable
 FM 458-1 DP: 1XXX XXXX = TRUE
0XXX XXXX = FALSE
In order to achieve high processing speeds with 32-bit accesses, the
following must be ensured by appropriately configuring the FM 458-1
DP/CFC (offset, refer below) as well as programming the SIMATIC-CPU,
so that
 16-bit values (INT/WORD data types)
are saved at even addresses (word limits) and
 32-bit values (REAL, DINT data types)
at addresses which are divisible by 4 (double word limits)
are saved in the two P-bus memories which are 128 bytes large.
Application
Blocks and
transfer commands
CFC data type
“BOOL“
Data save