Data Coherency In Communications Windows - GE PACSystems RX7i Reference Manual

Chapter 4. CPU Operation
4.4

Data Coherency in Communications Windows

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: 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 transitioned from Stop to
Run.
148 PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual GFK-2222AD