98
Rockwell Automation Publication 1756-UM540E-EN-P - December 2017
Chapter 5
1756-OF8I Isolated Analog Output Module
Redundant Owners
Redundant ownership lets a single controller use redundant adapters to
communicate with a single output or lets two separate controllers coordinate to
control the output.
Configure 1756-OF8I Redundant Owners
To enable Redundant Ownership mode in the output module, each connection
to the output module is via a redundant owner module definition. In the module
definition, you select between Redundant Output Owner A and Redundant
Output Owner B. Each pair of connections must have an A and a B requested—
that is, if the first is A, the second must be B.
If the second connection does not pair with the original connection, it is rejected
with a general status = 0x01 and extended status = 0x031D. All other aspects of
configuration between the two connections must be identical.
After the connection is established, a redundant owner uses the Claim Owner
Output (COO) tag to indicate that it is ready for ownership of the outputs. The
Ready Owner Output (ROO) tag indicates that an owner is ready to take
ownership if needed. The ROO is implemented as a single bit, OwnerReady, as
this implementation is intended for only two controllers.
When the OwnerClaim bit is set, it indicates that the controller wants to claim
ownership of the redundant connection and have its outputs actively used. If
both redundant owners have COO set, the last originator application that
transitioned its COO flag from cleared to set is the owner.
If neither redundant owner has OwnerClaim set, then the controller that has the
OwnerReady bit set becomes the owner. If neither controller has OwnerClaim
set and both have OwnerReady set, owner A becomes the owner. If both
controllers have OwnerClaim=0 and OwnerReady=0, then the outputs go to
IDLE (Program mode).
Finally, the Input data adds status fields that indicate if the output module has an
active owner (OwnerActive) and for which controller, A or B (OwnerID). For
each of owner A and B, three status fields indicate if the controller is connected
(OwnerAConnected/OwnerBConnected) and echo the output values received
for each owner via OwnerAClaim/OwnerBClaim and OwnerAReady/
OwnerBReady, respectively.
TIP
Only a received 0-to-1 transition, and not simply the receipt of a new
connection, is considered such a transition for ownership.
