Allen-Bradley SLC 500 DeviceNet, User Manual, Page: 104 / 139

Publication 1747-6.5.5 - August 2000
A-4 Data Map Example
Example Output Mapping
Scheme
This example’s output mapping scheme is a simplified and fixed map
of the discrete outputs and data from the device output data table to
DeviceNet devices.
Devices present in the default database are strobed only; therefore,
the output data-map bits are mapped into each network’s strobe
message. If the discrete table is available, it serves as a source for the
strobe bits; otherwise, the source is found in M1/M0 file transfer
locations.
Example Characteristics
•
strobe is used to send output to the DeviceNet devices
•
poll is disabled
•
one output data bit each is sent to nodes 1-62
•
the output data bits are embedded in the 8 byte (64 bit) data
portion of the DeviceNet strobe message
•
the output bit string source within the strobe message is divided
across the discrete outputs in the scanner’s discrete output data
table
Example Framework
This example adheres to the following structure:
•
when a 1747-SDN is running this configuration, there cannot be
any other 1747-SDN or 1771-SDN on that network
•
DeviceNet devices may reside only at nodes 1-62
•
address 0 must be used for the scanner
•
the first word in the device output-image data table always
contains the module command word (this is applicable under
any mapping scheme)
•
output bits received from processor for nodes 1-62 are mapped
to the scanner’s discrete output data table
The following illustrates an output-data mapping scheme example for
the 1747-SDN scanner. Output bits are mapped from the processor’s
output image table, to the scanner’s output data table, and to each
device via strobe message.