Use Of Free Channels On An Existing Module - Siemens SIMATIC S7-400H Manual

Result
The fault-tolerant system processes the entire system hardware with the new user
program in the Redundant system mode.
10.2.8

Use of free channels on an existing module

The use of previously free channels of an I/O module depends primarily on
whether or not parameters can be assigned to the module.
Modules to which parameters cannot be assigned
In the case of modules to which parameters cannot be assigned free channels can
be connected and used in the user program at any time.
Modules to which parameters can be assigned
In the case of modules to which parameters can be assigned the hardware
configuration must be modified to the sensors or actuators to be used. This
generally necessitates reassignment of parameters to entire module.
It is then no longer possible to operate the module concerned without interruption.
One-way output modules briefly output 0 (instead of the configured substitute or
holding values).
New parameters are not assigned to modules in switched DP stations on
switching to the CPU with the modified configuration. To change the channel
usage the following procedure is required:
– In steps I to VI (see Section 10.3) the module concerned is completely
removed from the hardware configuration and the user program. However, it
can remain plugged into the DP station. The module drivers must not be
removed.
– In steps 2 to 7 (see Section 10.2) the module is added to the hardware
configuration and the user program again with the changed use.
Warning
!
Modules concerned will not be addressed between the two switching processes
(steps V and 5); affected output modules output the value 0. The existing channel
drivers in the user program retain their signals.
If this reaction cannot be tolerated for the process to be controlled then it is not
possible to use previously free channels. In this case you must plug in additional
modules in order to expand the system.
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Modifications to the System while in Operation
10-15