Data Coherency In Communications Windows - GE PACSystems RXi User Manual

Data Coherency in Communications Windows

5.4
When running in Constant or Limited Window mode, the Controller and Backplane
Communications Windows may be terminated early in all CPU sweep modes. If an external
device, such as CIMPLICITY HMI, is transferring a block of data, the coherency of the data
block may be disrupted if the communications window is terminated prior to completing the
request. The request will complete during the next sweep; however, part of the data will have
resulted from one sweep and the remainder will be from the following sweep. When the CPU
is in Normal Sweep mode and the Communications Window is in Run-to-Completion mode,
the data coherency problem described above does not exist.
Note:
GFK-2816F
External devices that communicate to the CPU while it is stopped will read
information as it was left in its last state. This may be misleading to operators viewing
an HMI system that does not indicate CPU Run/Stop state. Process graphics will
often indicate everything is still operating normally.
Also, note that non-retentive outputs do not clear until the CPU is changed from Stop
to Run.
August 2015
Chapter 5. CPU Operation
79