Digital Signal Processing Reference
In-Depth Information
An FPGA-based "virtual" train simulation will be used that emulates this setup
and provides video output. Since there are no actual power circuits connected
to a train on the FPGA board, it is only intended to give you a visual indication
of how the output signals work in the real system. The following sections
describe how the state machine should control each signal to operate the trains
properly.
8.2 Train Direction Outputs (DA1-DA0, and DB1-DB0)
The direction for each train is controlled by four output signals (two for each
train), DA (DA1-DA0) for train A, and DB (DB1-DB0) for train B
2
. When
these signals indicate forward “01” for a particular train, a train will move
counterclockwise (on track 4, the train moves toward the outer track). When the
signals imply reverse “10”, the train(s) will move clockwise. The “11” value is
illegal and should not be used. When these signals are set to “00”, a train will
stop. (See Figure 8.2.)
DA = 01 : Train A Moves Forward
(counterclockwise)
Switch 3
Track 1
Track 3
Sensor 5
Sensor 1
Sensor 2
Sensor 3
Sensor 4
Track 4
Track 2
Switch 1
Switch 2
Figure 8.2
Controlling the train's motion with the train direction signals.
2
For those familiar with earlier editions of this topic, additional track power signals were required for
power control relays. This new train problem is based on newer digital DCC model trains and it no longer
needs the track power signals and relays, so they have been eliminated. The signals work exactly the same
as the previous train setup, if you assume that track power supply A always runs train A and track power
supply B always runs train B.
