Rockwell Automation DEVICENET 1771-SDN, User Manual

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Publication 1771-6.5.132 - June 2000
Before You Begin 1-5
The concept described below applies to both input and output data
tables. For example, when using your 1771-SDN in 1-slot addressing
mode, you have eight bits of discrete input
and
eight bits of output
available.
The address density is set via dip switches on the 1771-SDN module
and 1771 chassis. For more information about setting your module’s
address density with switches, refer to the 1771-SDN Scanner Module
Installation Instructions, publication 1771-5.14. For more information
about 1771-module addressing, refer to chapter 3 and to your PLC
programmable controller system-level installation manual and design
manual.
In the scanner’s input and output data tables, there is one byte of memory that is
reserved for communication between the processor and the scanner.
Processor-specific responses from the scanner are read by the processor in this byte
of the input data table. Scanner-specific instructions are written to this byte of the
output data table.
In 2-slot addressing mode, the only memory that would have
been available for discrete data transfer (8 bits) is taken up by
scanner/processor communication.
0 bits for discrete data transfer 2-slot addressing
8 bits for discrete data transfer
1-slot addressing
24 bits for discrete data transfer 1/2-slot addressing
In 1-slot addressing mode, there are 16 bits: eight bits for
scanner/processor communication, and eight bits for discrete
data transfer.
In 1/2-slot addressing mode, there are 32 bits: eight bits used for
scanner/processor communication, and 24 bits for discrete data
transfer.
= bits reserved for 1771-SDN and
processor communication
= bits available for discrete
data transfer
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