Month: August 2026

Front Panel Unit (FPU)

The Front Panel Unit (FPU) contains the necessary connectors, switches,

logic, and LED indicators for the Front Panel. For every type of Trusted I/O

Module, the FPU contains the Slice Healthy, Active/Standby, the Educated

LED indicators, and the Module removal switches. Additional bicolor LEDs

provide status indication for the individual I/O signals. Serial data interfaces

connect the FPU to each of the HIU slices to control the LED status indicators

and monitor the Module removal switches.

Host Interface Unit (HIU)

The HIU is the point of access to the Inter-Module Bus (IMB) for the Module.

It also provides power distribution and local programmable processing

power. The HIU is the only section of the I/O Module to directly connect to the

IMB Backplane. The HIU is common to most high integrity I/O types and has

type dependent and product range common functions. Each HIU contains

three independent slices, commonly referred to as A, B, and C.

All interconnections between the three slices incorporate isolation to help

prevent any fault interaction between the slices. Each slice is considered a

Fault Containment Region (FCR), as a fault on one slice has no effect on the

operation of the other slices.

The HIU provides the following services common to the Modules in the

family:

• High-Speed Fault Tolerant Communications with the TMR Processor

via the IMB interface.

• FCR Interconnect Bus between slices to vote incoming IMB data and

distribute outgoing I/O Module data to the IMB.

• Galvanically isolated serial data interface to the FIU slices.

• Redundant power sharing of dual 24 Vdc chassis supply voltage and

power regulation for logic power to HIU circuitry.

• Magnetically isolated power to the FIU slices.

• Serial data interface to the FPU for Module status LEDs.

• SmartSlot link between Active and Standby Modules for coordination

during Module replacement.

• Digital Signal Processing to perform local data reduction and

self-diagnostics.

• Local memory resources for storing Module operation, configuration,

and field I/O data.

• Onboard housekeeping, which monitors reference voltages, current

consumption and board temperature.

Field Interface Unit (FIU)

The Field Interface Unit (FIU) is the section of the Module that contains the

specific circuits necessary to interface to the particular types of field I/O

signals. Each Module has three FIUs, one per slice. For the TMR 24 Vdc Digital

Output Module, the FIU contains one stage of the output switch structure,

and sigma-delta (ΣΔ) output circuit for each of the 40 field outputs. Two

additional ΣΔ circuits provide optional monitoring of the external field I/O

supply voltage.

The FIU receives isolated power from the HIU for logic. The FIU provides

additional power conditioning for the operational voltages required by the

FIU circuitry. An isolated 6.25 Mbit/sec serial link connects each FIU to one of

the HIU slices.

The FIU also measures a range of onboard “housekeeping” signals that assist

in monitoring the performance and operating conditions of the Module.

These signals include power supply voltages, current consumption, onboard

reference voltages and board temperature.

Field Termination Unit (FTU)

The Field Termination Unit (FTU) is the section of the I/O Module that

connects all three FIUs to a single field interface. The FTU provides the Group

Fail-Safe Switches and passive components necessary for signal conditioning,

overvoltage protection, and EMI/RFI filtering. When installed in a Trusted

Controller or Expander Chassis, the FTU field connector interconnects to the

Field I/O Cable Assembly attached at the rear of the Chassis.

The SmartSlot link is passed from the HIU to the field connections via the

FTU. These signals go directly to the field connector and maintain isolation

from the I/O signals on the FTU. The SmartSlot link is the intelligent

connection between Active and Standby Modules for coordination during

Module replacement.

Description

The TMR 24 Vdc Digital Output Module is a member of the Trusted range of

input/output (I/O) Modules. All Trusted I/O Modules share common

functionality and form. At the most general level, all I/O Modules interface to

the Inter-Module Bus (IMB) which provides power and allows communication

with the TMR Processor. In addition, all Modules have a field interface that is

used to connect to Module-specific signals in the field. All Modules are Triple

Modular Redundant (TMR).

All High Integrity I/O Modules are made up of four sections: Host Interface

Unit (HIU), the Field Interface Unit (FIU), the Field Termination Unit (FTU),

and the Front Panel Unit (or FPU).

Features

• 40 Triple Modular Redundant (TMR) output points per Module.

• Comprehensive, automatic diagnostics and self-test.

• Automatic line monitoring per point to detect open circuit and short

circuit field wiring and load faults.

• 2500V impulse withstand opto/galvanic isolation barrier.

• Automatic overcurrent protection (per channel), no external fuses

required.

• Onboard Sequence of Events (SOE) reporting with 1 ms resolution.

• Module can be hot-replaced online using dedicated Companion

(adjacent) Slot or SmartSlot (one spare slot for many Modules)

configurations.

• Front Panel output status light-emitting diodes (LEDs) for each point

indicate output status and field wiring faults.

• Front Panel Module status LEDs indicate Module health and

operational mode (Active, Standby, Educated).

• TϋV Certified IEC 61508 SIL 3.

• Outputs are powered in isolated groups of eight. Each such group is a

Power Group (PG).