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4-14 Field Control™ Genius® Bus Interface Unit User’s Manual
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October 1999 GFK-0825F
4
Operation of the BIU with a Micro Field Processor
The Micro Field Processor (MFP) is a specialized Micro PLC that provides local input/output logic
within a Field Control I/O station. The MFP itself does not perform an I/O scan; that function is
performed by the BIU.
MFP and BIU Synchronization
Automatic operation of the Micro Field Processor must be synchronized with that of the BIU.
Synchronization between the MFP and the BIU occurs at the following points:
1. The MFP waits for group data from the BIU.
2. The MFP waits for its input reference parameter data (see page for a discussion of reference
parameter data) from the BIU. After receiving the reference parameter data from the BIU, the
MFP solves its logic program.
3. After solving its logic program, the MFP waits for the BIU to request its output reference
parameter data. Or, if the MFP is still busy, the BIU waits for the Micro Field Processor to
finish solving its logic.
4. The MFP waits for the BIU to request any group data from the MFP.
The diagram on the next page shows the basic points of synchronization between a BIU and an
MFP. The Micro Field Processor always performs housekeeping and programmer window
functions regardless of the combination of BIU and MFP modes.
MFP I/O References
The MFP itself has the following configurable references:
I001 to I512
Q001 to Q512
AI001 to AI128
AQ001 to AQ128
References used by the host may map to these MFP references, although that is not necessary.
Appendix D gives examples of I/O reference assignments.
MFP Operating Modes
In the
Standard Program Sweep
mode, the Micro Field Processor executes each sweep as quickly
as possible with a varying amount of time consumed each sweep.
In the
Constant Sweep Time
mode, each sweep consumes the same amount of time. This time is
configurable to be from 5 to 200 milliseconds.
When the MFP is in
Stop
mode, the application program is not executed. In this mode, it is
possible to choose whether or not the I/O is scanned (internally, by the MFP) and whether
communications with the programmer will continue.
If the BIU requests data from the Micro Field Processor while the MFP is in Stop Fault mode, the
requested data will either be defaulted or held in its last state, depending on the configuration of the MFP.
In Stop-No I/O mode, the MFP updates its internal I/AI tables with data received from the BIU,
and sends zeros for all data (reference or group) to the BIU.