DESCRIPTION AND OPERATION
MPI MODULE OPERATION
I-E96-203C
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I/O Expander Bus
The I/O expander bus interface is implemented using an
Elsag Bailey-designed integrated circuit. The microprocessor
can select one of two modes of operation: DMA or auto mode.
The MFP software selects the mode of operation for the I/O
expander bus. Mode selection is based on optimizing the
number of bytes to be transferred. In either mode of opera-
tion, the microprocessor does not need to wait for each byte
to transfer (as in previous controllers). The transfer rate is
programmable in software and optimizes the data transfer
rate according to the number of I/O modules attached to the
MFP module.
The MFP module connects to the I/O expander bus through
the backplane of the module mounting unit. It is an eight-bit
parallel bus that provides the communication path for I/O
data from I/O modules. The I/O expander bus supports 64
low power I/O modules (both INFI 90 and Network 90).
I/O Section
The I/O section interface allows the microprocessor to read
the switches that tell it how to operate and set the module
address. This section also contains latches whose outputs
connect to the status and error LEDs. This section monitors
redundant modules and outputs a signal to the LEDs of the
primary module. Upon failover, this output de-energizes and
the output of the backup module energizes as it takes over.
Additionally, the I/O section monitors the stop/reset push-
button. When the pushbutton is pressed, the I/O section
insures that the module completes any I/O functions before
it stops the module.
The MFP module provides only data and control signals for
auxiliary I/O. Any necessary circuitry for the serial ports or
station link is on the IMMPI01 Multi-Function Processor
Interface (MPI) Module. The connection between the MPI and
MFP modules is buffered. During normal operation, the MFP
module reads a status line from the MPI module to verify that
it is installed. If it is, the MFP module transfers module data
to and from the MPI module.
MPI MODULE OPERATION
The MPI module provides the MFP module with serial ports
and a station link. It contains standard I/O ports (i.e.,
RS-485, RS-232-C) that the MFP module can use. The MPI
module is an interface device that handles I/O to and from
the MFP module. Control and data signals from the MFP mod-
ule travel through a 60-pin ribbon cable to the MPI module.
