Considerations When Configuring Remote I/O; G File Considerations; Crossing Logical Rack Boundaries; Examples Of Crossing Logical Rack Boundaries - Allen-Bradley 1747-SN User Manual

4–10 Scanner Configuration and Programming
Considerations When
Configuring Remote I/O
Publication 1747 6.6 - July 1996
The following sections contain information that you must understand
before you configure your scanner's G file.

G File Considerations

You can only change the RIO configuration by modifying the G
file while offline in your program file. Your application program
cannot access the G-file, nor can you access it while online with
your programming device. However, your SLC control program
can dynamically inhibit and uninhibit RIO devices via the M0
file.
RIO devices larger than 1 logical rack appear as multiple devices
on the RIO link. Refer to the Crossing Logical Rack Boundaries
section below.
The address and size of the devices you list in the G file must
match the settings of each RIO device.

Crossing Logical Rack Boundaries

You express remote I/O image boundaries in an even number of
groups. For example, the 1747-ASB image can be any size from two
logical groups up to 32 logical groups (four logical racks), in 2
logical group increments.
If the scanner image assigned to an adapter is greater than 8 logical
groups (one logical rack), the image crosses logical rack boundaries.
If the scanner image assigned to an adapter is less than 8 logical
groups, it too can cross a logical rack boundary depending upon the
starting logical group number. The significance of crossing logical
rack boundaries is discussed in the next section.

Examples of Crossing Logical Rack Boundaries

Examples 1 and 2 that follow show adapters with logical image sizes
that cross logical racks 0 and 1. The image size of the adapter in
example 1 consumes all of logical rack 0 (eight logical groups) and
half of logical rack 1 (four logical groups). The image size of the
adapter in example 2 consumes two groups in logical rack 0 and four
groups in logical rack 1.