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45Chapter 3 Remote I/O Scanner Operation
I/O Scanner Memory
The Remote I/O Scanner has %I, %AI, %Q, %AQ, and %R internal memories. The
following table shows how much memory of each type the Remote I/O Scanner has,
and the maximum amount that may be transferred with the host.
Memory Type References Available in
Remote I/O Scanner
Transferred with Host
%I 12K up to 1024 bits
%Q 12K up to 1024 bits
%AI 8K up to 64 words
%AQ 8K up to 64 words
%R 16K not transferrable
I/O Memory in the Remote I/O Scanner
The Remote I/O Scanner’s %I, %AI, %Q, and %AQ memories are used for the remote
drop’s I/O data. They can also be used for data being transferred between the host and
option modules in the remote drop.
Individual I/O modules may be configured anywhere within available memory. If data
are to be exchanged with the CPU, the modules must be placed inside the configured
I/O map. Any I/O modules configured outside the I/O map will be scanned by the
Remote I/O Scanner, but the data will not be derived from or supplied to the CPU.
Configuring I/O References in a Series 90–70 PLC Application
When configuring I/O references for a Series 90–70 PLC:
1. A Logicmaster 90 program folder for the Series 90–70 contains the I/O map for
each remote drop.
2. A Logicmaster 90 program folder for a Remote I/O Scanner also contains an I/O
map.
3. For 90–70 applications, it recommended that both of these I/O maps agree.
4. The configured data lengths must agree.
For most applications, matching PLC and Remote I/O Scanner references are
recommended to avoid confusion. However, it is not mandatory to assign the same
references in the Remote I/O Scanner configuration and in the PLC configuration.
%R Memory in the Remote I/O Scanner
The Remote I/O Scanner has 12K bytes of %R memory that is not used for data
transfer with the host. However, it is available for other uses such as transferring data
with Programmable Coprocessor Modules in the remote drop.