Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 336)

Preface MicroLogix 1000 Programmable Controllers User Manual
D–8
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 processor. File ownership prevents other devices from reading from or
writing to the processor while the download is in process. If the controller were to
respond to a device’s read commands during the download, the processor 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 processor 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 to greater 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 processor and try the program download
again. The only other way to clear file ownership is to cycle power on the
processor.