Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 213)

Publication AG-UM008C-EN-P - February 2005
Configuring MicroLogix 1000 Controllers 6-9
Ownership Timeout
When a program download sequence is started by a software package
to download a ladder logic program to a MicroLogix controller, the
software takes file ownership of the controller. File ownership
prevents other devices from reading from or writing to the controller
while the download is in process. If the controller were to respond to
a device’s read commands during the download, the controller could
respond with incorrect information. Similarly, if the controller were to
accept information from other devices, the information could be lost
because the program download sequence could immediately
overwrite the information. Once the download is completed, the
programming software returns the file ownership to the controller, so
other devices can communicate with it again.
With the addition of DF1 half-duplex slave protocol, the controller
clears the file ownership if no supported commands are received from
the owner within the timeout period. If the file ownership were not
cleared after a download sequence interruption, the controller would
not accept commands from any other devices because it would
assume another device still had file ownership.
If a download sequence is interrupted, due to noise caused by
electromagnetic interference, discontinue communications to the
controller for the ownership timeout period and restart the program
download. The ownership timeout period is set to 60 seconds as a
default for all protocols. However, if you are using DF1 half-duplex
and the poll timeout value is set higher than 60 seconds, the poll
timeout value will be used instead of the ownership timeout. After the
timeout, you can re-establish communications with the controller and
try the program download again. The only other way to clear file
ownership is to cycle power on the controller.