Technical data

Appendix
27.7 Accessing Process and I/O Data Areas
Programming with STEP 7
674 Manual, 05/2010, A5E02789666-01
27.7 Accessing Process and I/O Data Areas
27.7.1 Accessing the Process Data Area
The CPU can access inputs and outputs of central and distributed digital input/output modules
either indirectly using the process image tables or directly via the backplane/P bus.
The CPU accesses inputs and outputs of central and distributed analog input/output modules
directly via the backplane/P bus. You can also enter the addresses of analog modules in the
process image area.
Addressing Modules
You assign the addresses used in your program to the modules when you configure the modules
with STEP 7, as follows:
• With central I/O modules: arrangement of the rack and assignment of the modules to slots in
the configuration table.
• For stations with a distributed I/O (PROFIBUS DP or PROFINET IO): arrangement of the DP
slaves or IO devices with the PROFIBUS address or device name and assignment of the
modules to slots.
By configuring the modules, it is no longer necessary to set addresses on the individual modules
using switches. As a result of the configuration, the programming device sends data to the CPU
that allow the CPU to recognize the modules assigned to it.
Peripheral I/O Addressing
There is a separate address area for inputs and outputs. This means that the address of a
peripheral area must not only include the byte or word access type but also the I identifier for inputs
and Q identifier for outputs.
The following table shows the available peripheral address areas.
Address Area Access via Units of Following Size S7 Notation (IEC)
Peripheral (I/O) area: inputs Peripheral input byte
Peripheral input word
Peripheral input double word
PIB
PIW
PID
Peripheral (I/O) area:
outputs
Peripheral output byte
Peripheral output word
Peripheral output double word
PQB
PQW
PQD
To find out which address areas are possible on individual modules, refer to the following manuals:
• CPU 31xC and CPU 31x, Technical Data
• S7-400 Programmable Controllers, CPU Data