Rockwell Automation T7404 ICS Regent+Plus AC Digital Input Module 110VAC - Manual (Page 3)

(T7404) AC Digital Input Module
P D - 7 0 1 3 M a r - 0 6
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module (preventing I/O Safetybus failures upstream from the
module from affecting its ability to be read). The voted result
is then passed to the I/O bus interface logic.
After receiving the voted data read request, the I/O bus
interface logic sends its input data to the module’s three bus
drivers. Each of the three bus drivers is independently
powered and controlled by the I/O transceiver modules—
preventing failures in a single driver from propagating to the
other two busses.
The bus drivers transmit the data across the backplane I/O
Safetybus to the I/O transceivers which, in turn, transmit the
data to the processors.
Testing and Diagnostics
Each module’s voter circuits are periodically tested by the
processor modules. Discrepant data are sent through one of
three legs of the I/O Safetybus to determine whether the
module’s voter is able to outvote the incorrect data. A failure
to return the correct majority-voted result to the processors
produces an I/O module error indication at the processor
modules and a module fault indication at the I/O module.
Each type of module has a unique identification code that is
read by the controller. This code lets the controller know
which type of module is installed in each I/O chassis slot and
how to address that module and its points specifically. If a
module is removed, or is replaced with a module of a different
type, the processor modules will indicate I/O module errors.
Loopback logic tests periodically write data to the module and
then read it back to determine whether the module’s I/O bus
interface logic is functioning correctly.
Front Panel Indicators
Figure 2 shows the physical features of the AC digital input
module. The front panel of each module contains active and
fault status indicators and field signal status indicators for
each circuit.