Rockwell Automation T3411 ICS Regent Monitored Digital Input Modules - Manual (Page 3)

Monitored Digital Input Modules (T3411)
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wired back to the field power supply return. Optionally a line
monitor device can be connected across the input switch in the
field (as shown in Figure 1).
The input module monitors the voltage of the input circuit
after the internal dropping resistor, comparing it to a
reference voltage generated by the D/A converter inside the
module. The comparator generates an on or off state
depending on which voltage signal is greater than the other.
The field-side FPGA controls and monitors the reference
voltage signal and reads the status of all 16 input
comparators. This information is stored and sent through
optical isolation to the logic-side FPGA. The logic-side FPGA
interfaces the input data to the I/O Safetybus and drives the
module’s front panel status LEDs.
Testing and Diagnostics
Standard I/O Module Testing
The processor modules send triplicated read data requests to
the input module over the I/O Safetybus. The processors’
addressing data and data read requests are voted by the
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
controlled — preventing failures in a single driver from being
propagated into the rest of the system.
The bus drivers then move the data onto the I/O Safetybus
which, in turn, passes it to the processors.
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.