Technical data

3.3.2.1 Global I/Os (GP)
The term "global I/Os" means that part of the I/O area is not used by I/O
modules but for global data exchange between SIMATIC PLCs. Global data
exchange involves the CP sending the entire changed output area assigned
to the global I/Os and cyclically updating the entire input area assigned to
the global I/Os with the received data once again. The global I/O area is in
the I/O area of the controller and is also used by the PLC program. The
address areas are processed with STEP 5 operations. The mode can either
be synchronized with the cycle or free. With the cycle-synchronized mode, a
CP-HDB must be called at the checkpoints required by the user to ensure
the consistency of inputs and outputs. This HDB also triggers a group job
for data transmission.
An important characteristic of global I/Os is that changes in the data bytes
are recognized and only the changes transmitted.
This data transmission is suitable for the transfer of single bytes between
active SIMATIC S5 programmable controllers.
The CP 5430 TF/CP 5431 FMS uses the SDN transmission service to
transmit the data "packed" in a frame via the SINEC L2 bus.
The basic procedure for this communication is explained in Chapter 9.
Fundamentals of the Model B8976060/02
Volume 1 3 - 16