As explained on the New DCC System page, DTC-8 boards show track occupancy. These feed into a CANACE8C (kit 89) which acts as a “producer” to send messages via CBUS to a CANLED (kit 82). Attached to the CANLED is a TM4 test board (kit 901) populated with LEDs to show an approximation of the track diagram. As a locomotive moves around the layout, its position can be seen on the TM4.