The programming inside a Microlok unit is called vital programming because it controls safety-critical railroad signal functions.
This logic must make sure that trains are protected from unsafe conditions such as conflicting routes, signals clearing incorrectly, switches moving at the wrong time, or trains being authorized into an occupied track.
Microlok programming uses proprietary software and a special programming language developed for railroad signal control.
The system was originally developed by GRS and is now associated with Wabtec. Because the system is safety-critical, access to the programming tools and logic is controlled.
The Microlok programming language is considered high-level because it allows signal engineers to work with railroad signal terms instead of only low-level computer code.
Engineers can build logic using familiar concepts such as routes, signals, switches, track occupancy, route locking, approach locking, time locking, and signal aspects.
Microlok logic is designed with safety as the main priority. The program must only allow safe signal and switch conditions.
For example, a signal should not clear unless the route is lined, locked, unoccupied, and protected against conflicting movement.
Engineers use a Microlok development environment to write, review, simulate, test, and compile the vital logic.
This environment helps verify that the programmed logic follows the intended signal design and does not create unsafe operating conditions.
Simulation tools allow engineers to test the logic before it is placed into service. This helps confirm how the system responds during normal operation, route requests, signal clearing, train occupancy, failures, and abnormal conditions.
Simulation does not replace field testing, but it helps catch logic problems before equipment is installed or commissioned.
Microlok programming tools are not open to everyone. Only trained and authorized personnel should develop or modify vital logic.
This protects the safety of the railroad by controlling who can make changes to the logic that controls train movement.
After programming is completed, the logic must be tested in the field. Field verification confirms that the software logic matches the plans and that inputs, outputs, signals, switches, and track circuits operate correctly.