Technical data

An important characteristic of the global I/Os is that changes in the data
bytes are recognized and only these changes transmitted. The changed
data bytes are then transmitted more quickly compared with data
transmission using HDBs (refer to Chapter 7).
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 GP and updating the entire input area assigned to the GP with the
received data once again cyclically. You can use these I/Os as normal
inputs and outputs. 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, an HDB must be called at the checkpoints
required by the user to ensure the consistency of inputs and outputs.
Ideally with the global I/Os, you should transmit data which change rarely
relative to the target rotation time (the rate of change should be a multiple
of the target rotation time). If, however, the data bytes to be transmitted
change constantly (compared with the target rotation time), the advantage
of minimum bus load, the main characteristic of GP, is lost.
☞
Simultaneous use of GP and DP is not possible.
Communication with Global I/Os B8976060/01
Volume 1 9 - 2