Rockwell Automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual - Manual (Page 36)

36 Publication 1769-UM009E-EN-P - August 2009
Chapter 4 Automatically Configure a DeviceNet Network
How AutoScan Operates AutoScan is active when the feature is enabled and the scanner is in IDLE
mode. When active, the scanner attempts to connect to each device not
enabled in the scan list. The scanner only checks for devices with node
addresses between 0 and 61, inclusive. The connections to these devices are
made on a round robin basis.
When a device is found, the scanner gets the Produced and Consumed data
sizes from the slave devices's Connection Object instance(s).
• If the Produced data size is greater than the configured I/O allocation
size, the device is added to the scanlist with a produced size set equal to
the I/O allocation size.
When this happens, an I/O connection is made with the device. But it
errors and error code #77 is displayed on the 1769-SDN for the device’s
node number.
• If the Consumed data size is greater than the configured I/O allocation
size, then the node is rejected and not entered into the scan list.
However, you can change the I/O allocation size, as described in Configure I/O
Allocation Size Via the User Program , to accommodate the device with the largest
Produced and Consumed data sizes in your scanlist.
For qualifying nodes, the scanner enters the device into the scan list and
attempts to allocate an I/O connection using one of the following
communication format choices, in this particular order:
• Change Of State (COS) EPR = 250ms
• Poll EPR = 75ms
• Strobe EPR = 75ms
• Cyclic EPR = 500ms
EXAMPLE
If a photoeye was connected on a network that only supported
strobed connections, the scanner does a couple of things.
• First, the scanner recognizes that a device exists for which
memory was available for the node number with the
configured allocation size on a network that was not
currently mapped.
• Then, the scanner would attempt to initiate both COS and
polled connections first, but the strobed connection would
be selected as that is the only connection that the photoeye
supported.