Functional decomposition

As mentioned in the previous paragraph, control/command is implemented in the train via residual hard-wired logic on the one hand, and programmable logic on the other. This programmable part is usually grouped together in a subsystem called TCMS (Train Control and Monitoring System).

Depending on the geography of the rail market, the market segment and the manufacturers involved, the scope and technical content of TCMS may vary, but its foundations and raison d'être remain invariable, defining it as the train's "nervous system".

The TCMS is an on-board computer system that connects, controls and monitors all the electronic subsystems required to fulfill the mission assigned to the equipped train....