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49Chapter 3 Remote I/O Scanner Operation
Configuring Extra References
Normally, there are no extra references configured for the Remote I/O Scanner, since
that would consume extra references in the host CPU, making them unavailable for
other modules. In addition, extra references add to the Genius bus scan time, so they
should be avoided if they are not actually needed.
However, reserving extra references or leaving vacancies at configuration time is a
convenient way to prepare for future additions to a remote drop. (If Logicmaster
90–70 is used for configuration, unused references may be placed anywhere in the
input message).
Input Data Message with Some Inputs Not Used
discrete inputs analog inputs
Configured %I Length Configured %AI Length
%AI starting reference data%I starting reference data
To CPU
unused
discrete
references
unused
analog
references
Example
An application has two remote drops, which have been configured as #016 and #017.
Drop 016
Drop 017
%I0001 – %I0064
%AI0001 – %AI0008
%Q0001 – %Q0032
%AQ0001 – %AQ0008
%I0065 – %I0128
%AI0009 – %AI0016
%Q0033 – %Q0064
%AQ0009 – %AQ0016
At a later time, it becomes necessary to add a 32–point input module to drop 016.
However, in drop 016, there are already enough input modules to use all of the
assigned input references (%I0001 – %I0064). Ideally, the extra modules would be
added to remote drop 016 at %I00065, but this is already used as a reference in drop
017. The alternatives at this stage are:
1. Change the map of drop 017 to free up %I0065 – %I0096.
2. Change the map of drop 016 to start at higher references, such as %I0097 –
%I0160.
It would have been easier to add the module to drop 016 if extra references had been
configured originally, or if some vacancies had been allowed.
Drop 016
Drop 017
%I0001 – %I0096
%AI0001 – %AI0008
%Q0001 – %Q0032
%AQ0001 – %AQ0008
%I0097 – %I0160
%AI0009 – %AI0016
%Q0033 – %Q0064
%AQ0009 – %AQ0016