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4-18 Field Control™ Genius® Bus Interface Unit User’s Manual
–
October 1999 GFK-0825F
4
How the Network Backs Up MFP Outputs
This technique works because of the synchronization between the operations of the Bus Interface
Unit and the Micro Field Processor. The diagram below shows details of the BIU/MFP
synchronization process. The numbers on the left side are the same as the numbers on the
synchronization diagram.
Move all outputs within BIU network
map from the Genius communications
buffers to the BIU internal tables
Read all reference input parameters from
a Synchronization module
7
8
MFP provides data
to BIU
BIU Waits if
MFP is busy
Micro Field ProcessorBus Interface Unit
10
Send all outputs to conventional modules
The Bus Interface Unit receives output data for the backed-up output module(s) from the Genius
bus (step 7). In step 8, the BIU receives data from the Micro Field Processor. Any data with the
same reference assignments overwrites the data already received from the bus. When the BIU sends
outputs to I/O modules (step 10), it sends the most recent contents of the output references. If the
MFP has not provided fresh output data (for example, if the MFP has stopped communicating with
the BIU), the outputs from the network are sent to the modules instead. Note that this will not work
if MFP outputs are configured to default instead of Hold Last State, because selecting default
causes the BIU to write default values into the output references at step 8.