Triconex DO 3401 is Digital Output Module.The Digital Output (DO) Module contains the circuitry for three identical, isolated channels. Each channel includes a proprietary ASIC which receives its output table from the I⁄O communication processor on its corresponding main processor. DO Modules use special quad output circuitry to vote on the individual output signals just before they are applied to the load. 

This voter circuitry is based on parallelseries paths which pass power if the drivers for channels A and B, or channels B and C, or channels A and C command them to close; in other words, two out of three drivers are voted on. The quad output circuitry provides multiple redundancy for all critical signal paths, guaranteeing safety and maximum availability.The DO Module periodically executes an output voter diagnostic (OVD) routine on each point.