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Configuring
4.3.3 Data transfer via I/O accesses
Application
To transfer low data quantities: up to max. 128 bytes
Appropriate function blocks are available for each data transfer direction
Blocks and transfer
and for each data type to be transferred.
commands
Table 4-2
The 8-bit CFC data type "BOOL" is represented in the SIMATIC S7-CPU
CFC data type
"BOOL"
as "BYTE" data type. This means that the SIMATIC S7 user must
appropriately set or evaluate the decisive MSB (Most Significant Bit):
• S7-CPU:
• FM 458:
Data save
In order to achieve high processing speeds with 32-bit accesses, the
following must be ensured by appropriately configuring the FM 458/CFC
(offset, refer below) as well as programming the SIMATIC-CPU, so that
• 16-bit values (INT/WORD data types)
• 32-bit values (REAL, DINT data types)
are saved in the two P-bus memories which are 128 bytes large.
4-8
SIMATIC-CPU
Data type Transfer
command
(SL program)
BYTE
T PAB abs.addr.
INT
T PAW abs.addr.
DINT
T PAD abs.addr.
REAL
T PAD abs.addr.
BYTE
L PEB abs.addr.
INT
L PEW abs.addr.
DINT
L PED abs.addr.
REAL
L PED abs.addr.
Data types and the associated commands/blocks for peripheral accesses
bit variable
1XXX XXXX = TRUE
0XXX XXXX = FALSE
are saved at even addresses (word limits) and
at addresses which are divisible by 4 (double word limits)
FM 458
Write
CFC function
direction
block
!
S7RD_B
S7RD_I
S7RD_D
S7RD
"
S7WR_B
S7WR_I
S7WR_D
S7WR
Application Module FM 458 - User Manual
6DD1904-0AE0
Data type
BOOL
INT
DINT
REAL
BOOL
INT
DINT
REAL
Edition 12.2001
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