In article . com,
Boltar writes
Interesting site , but it doesn't explain how the ATO and ATP are
seperate if they both rely on the track codes.

They're different functions within the train.

The ATP relies on the four basic codes. It picks them up and, in
essence, generates a set of permissions to the rest of the train:
"can move", "can accelerate", "can start from station", "can start
within tunnel", "maximum speed is X". These are then combined with the
current state of the train to provide the two controls of "disable
motors" and "apply emergency brakes". Thus the ATP only ever stops the
train.

The ATO takes the permissions from the ATP box, the commands from the
command spots ("speed X", "coast", "brake"), distances from the
odometer, and the map of the railway stored within the Auto Driving Box,
to actually control the train. Thus if it sees the command spot "speed
40" from the track but "maximum speed is 25" from the ATO, it will
accelerate or brake to 25. It relies indirectly on the four basic codes,
but only via the ATP, not by picking them up itself.

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