Addressing Via The Fb Im308C Function Block - Siemens SIMATIC S5 Manual

IM 308-C – addressing, diagnostics and use of the FB IM308C
9.1.3

Addressing via the FB IM308C function block

Definition
Advantages
Restrictions
When should I use
the FB IM308C?
9-10
If you opt for addressing through the FB IM308C (FB 192) you use the
CP page area and the IM3/IM4 area to address the distributed inputs and
outputs.
This address area is known as the DP window; by default, it occupies the ad-
dress area (F)F800 to (F)F9FF
H
See Section 9.7 for an explanation of the parameters exported to the
FB IM308C for the individual functions.
The advantages of addressing via the FB IM308C are as follows:
You can always address inputs through the FB IM308C, irrespective of
whether or not you have assigned the address with COM ET 200
Windows.
The FB IM308C is ideal for addressing large data quantities as is the case
with operator panels, IM 308-C as DP slave, drives, for example.
Data can be saved directly to a data block or a bit memory address area –
no linear addresses are lost.
The FB IM308C permits mixed addressing. For example, if you have
large data quantities you can address the first byte with linear addressing
and address the remaining bytes via the FB IM308C.
In this case you use the first byte as coordination byte that for high-speed
cyclic queries. When this coordination byte shows that the data in the
remaining bytes has been updated, you can address them through the
FB IM308C. This mechanism cuts down on runtime in the application
program.
If you want to address more than one IM 308-C in multiprocessor mode,
you can assign a DP window to each IM 308-C. This significantly reduces
the complexity of addressing.
If you use the FB IM308C, bear the following in mind:
Access to inputs/outputs is faster when you use linear or page addressing
than when you use the FB IM308C for addressing.
If you have already addressed an output with linear or page addressing,
you cannot read or write this output through the FB IM308C. The
IM 308-C does not recognize any attempt to set this output through the
FB IM308C.
Use the FB IM308C when the scope of the DP slaves or the IM 308-Cs is
such that linear addressing is no longer adequate.
.
H
ET 200 Distributed I/O System
EWA 4NEB 780 6000-02a