Additional considerations regarding autoscan – Rockwell Automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual User Manual
Page 53
Publication 1769-UM009E-EN-P - August 2009
53
Automatically Configure a DeviceNet Network Chapter 4
Additional Considerations
Regarding AutoScan
The factory default setting for AutoScan is disabled for all products.
Make sure that input or output data memory size in the scanner is large
enough to accommodate the size required based on the number of nodes on
the network and the AutoScan I/O allocation size per node.
for an accurate maximum node count by allocation size.
TIP
Nodes 0…61 inclusive are scanned and added to the scanlist if
they are not already mapped and I/O space exists. For
maximum capacity for slave devices, the scanner node address
could be configured as node 62; node 63 could also be used but
to avoid duplicate node address issues with a new device, this
is not recommended.
IMPORTANT
According the ODVA DeviceNet Technical Overview, the
maximum number of nodes on a DeviceNet network is 64.
However, the normal useful number of slave nodes is 62
because:
• the DeviceNet scanner requires a node
and
• we recommend that you leave node 63 unused for devices
that are added to the network in the future.
If a network interface is used on the network, and the above
bullets are taken into consideration, then the useful number of
nodes becomes 61.
EXAMPLE
If the I/O allocation size per node is configured for 16 bytes and
there are 32 slave devices on the network (node addresses 1 -
32), AutoScan requires 16 bytes x 32 = 512 bytes (128 DINT) of
I/O space in both the scanner's input and output table.
Assuming it is a CompactLogix system, the maximum scanner
input data table size is 90 DINT and 90 DINT for output. The
required space exceeds what the 1769-SDN can support. The
user would need to adjust the I/O allocation size or reduce the
slave device count on the network to include all of the devices
in the scanlist.
Devices outside of the scanner's allowable I/O image space
will be rejected and will not be included in the scanlist.