S5-95F Rules for Failsafe Operation of an S5-95F
18.14 Addressing and Address Assignments
The S5-95F's I/Os are subdivided into onboard I/Os and external I/Os.
In order that it be possible to address specific inputs and outputs, the I/Os must be assigned
addresses. Please refer to Chapter 6 for details on addressing and address assignments.
The addresses of the onboard I/Os are fixed, and cannot be changed. The addresses of the external
I/Os are slot-dependent.
Address Assignment for External I/O Modules
When you mount an external I/O module in a slot on a bus unit, the module is immediately assigned
a slot number and consequently a fixed byte address in the process image I/O tables.
Connect the sensors and actuators either via a connector or to the terminal block of the bus units.
The terminal selected determines the bit address (channel number) of the input or output.
Figure 18-4. Address Assignment
I/O module
=
Process image I/O
tables in the PLC
Slot number
+
channel number
Control
program
Address in a
statement
Address in the
process image output
table
Address in the
process image input
table
Data flow from module - PLC
Addressing of Single-Channel External I/Os
Single-channel I/Os are never failsafe. In the user program, these I/Os must always be referenced
under the address under which they are used in the relevant subunit.
Addressing of Two-Channel, Failsafe External I/Os
Two-channel I/Os can be used only with failsafe onboard I/Os or with redundant failsafe external I/O
modules.
Note
You must always address failsafe external I/Os in the user program at the address where
they are used in subunit A (failsafe external I/Os have always an even-numbered byte
address)!
EWA 4NEB 812 6210-02
18-29
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