Rockwell Automation Publication 1756-UM004C-EN-P - June 2021 31
Chapter 3 Connect Redundant EtherNet/IP Adapters
The primary adapter is always active and is responsible for monitoring all
inputs and outputs, monitoring diagnostics in the system, and reading and
writing data to and from I/O simultaneously. The secondary adapter is waiting
to take over communication, if the primary switches over.
If there is a switchover, the IP address swapping between the primary adapter
and the secondary adapter takes no longer than 50 ms from the time of the
initiating fault. The secondary adapter is the new primary and handles all
communication. Depending on the RPI's configured, the observed switchover
time can appear longer. Transmission time imposed by network infrastructure
has to be considered when calculating overall switchover time. No connection
drops occur during this switchover process.
This IP address swap is transparent to the user. You can detect which adapter
the primary adapter is by examining the four character display indicator near
the top of each adapter. On the primary adapter, the network status indicator
is steady green. On the secondary adapter, the network status indicator flashes
green.
Once a swap occurs, the ‘new’ primary adapter remains the primary unless
there is a reason to swap over again. When the previous primary adapter is
reinserted or reconnected, both adapters start the qualification process again
with the adapter that was reconnected becoming the new qualified secondary.
Status Display Codes
Table 6 shows the different status codes that can appear on the adapter related
to the Redundant Adapter feature.
Table 6 - Primary and Secondary Operation Modes
Status Code Description
PwrUp Power Up/ Unknown
DS Disqualified secondary
QS Qualified secondary
PwQs Primary with qualified secondary partner
PwDS Primary with disqualified secondary
PwNS Primary with no secondary
DSwP Disqualified secondary with primary
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