Rockwell Automation DEVICENET 1771-SDN, Руководство пользователя

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1 Publication 1771-6.5.132 - June 2000
Appendix
D
Data Map Example
This appendix describes a basic mapping example that connects two
DeviceNet networks (channels A and B of the 1771-SDN scanner) to
62 simple sensor-type devices. Each device sends one data byte that
contains one data bit and one status bit.
These are given in response to a strobe message. With channel A
only, the scanner maps this data to the discrete I/O table if it is
available; otherwise, the data is mapped to block transfer locations.
See the 1771-SDN DeviceNet Scanner Installation Instructions (pub.
no. 1771-5.14) for details on using block transfer read and write
operations to communicate between your PLC-5 processor and
1771-SDN scanner.
Example Input
Mapping Scheme
This example’s input mapping scheme is a simplified and fixed map
of discrete input data and status bits for DeviceNet devices. It is
mapped to discrete inputs and the device input data table. An
example for each slot-addressing mode is given.
Example Characteristics
•
strobe is used to query DeviceNet devices
•
poll is disabled
•
Devicenet A and B ports are connected to separate networks
•
the input data bit is fixed and occupies the lowest-order bit in
the lowest-order byte of the strobe (bit #0)
•
one bit of status data is accepted from each node responding to
the strobe
•
the status data bit is fixed and occupies the next lowest-order bit
in the next lowest-order byte (after the input data bit) of the
strobe (i.e., bit #1)
•
input and status data bits accepted from each node are mapped
to discrete inputs and the device input data table of the scanner
•
input and status data bits accepted from each node are fixed and
predefined
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