Using Sfc14 And Sfc15 In Step7 - Siemens SIPROTEC 7SA522 Manual

4.5

Using SFC14 and SFC15 in STEP7

Peripheral I/O
access commands
SFC14, SFC15 and
consistent data
Universal module
SIPROTEC PROFIBUS-DP - Communication profile
C53000-L1840-B001-03
The S7-CPU can read data from the connected PROFIBUS-DP devices or write data
to these devices in the CPU program using peripheral access commands.
For reading a measured value (integer value, ref. to chap. 3.4) from a SIPROTEC
device the following command can be used:
L PIW x
X determines the address of the measured value in the peripheral addressing range
of the S7 CPU.
The above-named instruction has to be executed with the associated addresses e.g.
five times in order to read five measured values.
After reading, every value has to be processed or to be copied in a data block for later
processing in the S7 program:
L PIW x
T DB10.DBW y
...
Occasionally, the S7 system functions SFC14 (DPRD_DAT) and SFC15 (DPWR_-
DAT) shall be used for data transmission in the CPU program instead of peripheral
I/O access commands.
These functions presuppose however that the data from and to the PROFIBUS-DP
slave devices are configured as consistent blocks.
No consistent blocks are defined for configuration of the PROFIBUS-DP slaves of the
SIPROTEC devices with the modules to be adjusted (e.g. Module: "Input 16 Bytes",
ref. to chap. "Configuration data in the standard mapping" in the Bus mapping docu-
mentation of the respective SIPROTEC device) because:
• for transmission of data from and to the SIPROTEC device only data types with a
data size of one, two or four bytes are used in general (ref. to chap. 3),
• access to word values (two bytes, e.g. measured values) and double-word values
(four bytes, e.g. counters) is guaranteed as consistent automatically with associ-
ated peripheral access commands from the S7 CPU,
• access to data in consistent blocks is not possible with peripheral access com-
mands.
A "Universal module" is per default always offered in HW Config of STEP 7 at the
parameterization of modular PROFIBUS-DP slaves.
With the "Universal module" it is possible to enter configuration data (including consis-
tent blocks) independently of the module definitions in the GSD file.
The PROFIBUS-DP slave of the SIPROTEC devices accepts these configuration data
within the number of input and output data bytes fixed in the standard mappings
(including of consistent blocks up to a definite size, see below).
The SFC14 and SFC15 also can be used with that.
Note:
A consistent block for the PROFIBUS-DP slave of the SIPROTEC devices can contain
maximum 16 byte values or 16 word values.
PROFIBUS-DP - Parameterization in DIGSI
79