LEGO MINDSTORMS Robots Manual page 57

Page 59
Output Commands
NQC includes several commands for controlling the outputs of the RCX. You've already seen one of these, OnFwd, in our first simple example.
On(const outputs)
This command turns on the specified outputs. The outputs should be some combination of the constant values OUT_A, OUT_B, and OUT_C. Multiple outputs can be specified by adding them
together, as shown in the first example. When an output is turned on, its current power and direction are consulted to determine what actually happens.
Off(const outputs)
This command turns off the specified outputs, putting them in brake mode. For motors, this means that the motor shaft will be hard to turn.
Float(const outputs)
Float() is really a variation of Off(). No power is sent to the output, but the shaft of an attached motor will turn freely. This is a useful option if you want your robot to coast to a stop.
You can set the direction of outputs with the following three commands:
Fwd(const outputs)
Use this command to set the direction of the specified outputs to forward.
Rev(const outputs)
This command sets the direction of the specified outputs to reverse.
Toggle(const outputs)
To switch the direction of one or more outputs, use this command.
To determine the output power, use the following command:
SetPower(const outputs, expression speed)
This command sets the power of the given outputs. Any expression that evaluates to a value from one to seven can be used as the speed. You may use the constant values OUT_LOW (1),
OUT_HALF (4), and OUT_FULL (7) if you desire.
To fully determine an output's actions, you should set its mode, direction, and power explicitly. By default, all three outputs are set to full power and the forward direction. Therefore, calling On()
is enough to get the motors running.
NQC provides two handy "combination" commands:
OnFwd(const outputs)
This command turns on the specified outputs in the forward direction.
OnRev(const outputs)
This command turns on the specified outputs in the reverse direction.