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7-6
Communicating with Other Devices
Guidelines for Block-Transfer Messages
Distribute 1771 analog modules
across multiple chassis
Isolate different 1771 chassis on
different networks
Increase ControlNet
unscheduled bandwidth
Increase the system overhead
timeslice percentage
Mapping Tags
Distributing 1771 analog modules across multiple chassis reduces the number of
block-transfers that a single 1771-ACN or 1771-ASB module needs to manage.
Isolating different chassis onto different networks diversifies the communications so that no
single network or communication module has to deal with all of the communications.
If communicating over ControlNet, increase the amount of ControlNet unscheduled
bandwidth to permit additional time on the network for data exchange.
Increase the Logix5000 controller’s system overhead timeslice to allocate more CPU time to
communication processing from the continuous task.
A Logix5000 controller stores tag names on the controller so that other
devices can read or write data without having to know physical
memory locations. Many products only understand PLC/SLC data
tables, so the Logix5000 controller offers a PLC/SLC mapping function
that lets you map Logix tag names to memory locations.
• You only have to map the file numbers that are used in
messages; the other file numbers do not need to be mapped.
• The mapping table is loaded into the controller and is used
whenever a “logical” address accesses data.
• You can only access controller-scoped tags (global data).
When mapping tags:
• Do not use file numbers 0, 1, and 2. These files are reserved for
Output, Input, and Status files in a PLC-5 processor.
• Use PLC-5 mapping only for tag arrays of data type INT, DINT,
or REAL. Attempting to map elements of system structures may
produce undesirable effects.
• Use these file types and identifiers:
Publication 1756-RM094A-EN-P - May 2004
For this Logix5000 array type:
Use this PLC file identifier:
INT array
N or B
DINT array
L
REAL array
F