12 Controller Architecture
Trident Planning and Installation Guide
Input/Output Modules
The controller manages the data exchanged between the MP and the following I⁄O
modules:
• Analog Input Module
• Analog Output Module
• Digital Input Module
• Digital Output Module
• Pulse Input Module
• Solid-State Relay Output Module
Analog Input Module
On an AI Module, each channel measures the input signals asynchronously and
places the results into a table of values. Each input table is passed to its associated
MP using the corresponding I⁄O bus. The input table in each MP is transferred to
its neighbors across the TriBus. The middle value is selected by each MP and the
input table in each MP is corrected accordingly. In TMR mode, the mid-value data
is used by the application; in duplex mode, the average is used.
Each AI Module is guaranteed to remain in calibration for the life of the controller;
periodic manual calibration is not required.
Special self-test circuitry is provided to detect and alarm all stuck-at and accuracy
fault conditions in less than 500 milliseconds, typically. This safety feature allows
unrestricted operation under a variety of multiple-fault scenarios.
Analog Output Modules
AO Module receives three tables of output values, one for each channel from the
corresponding Main Processor. Each point on each channel has its own digital-to-
analog converter (DAC). One of the three channels is selected to drive the analog
outputs. The outputs of the selected channel are continuously verified by I⁄O loop-
back inputs from each point, which are read by all three channels. If a fault occurs
in the driving channel, the channel is declared faulty, is disabled, and a new channel
is selected to drive the field device. The selection of the driving channel alternates
among the channels so that all three channels are periodically tested.
Each AO Module is guaranteed to remain in calibration for the life of the
controller; periodic manual calibration is not required.
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