NXC (and NBC)

NXC (Not eXactly C) is a language similar to NQC, which was the most popular way to program the RCXBuilt on NBC, the Next Byte Code ‘assembler’Uses the built in firmware, and p-code system

NXC uses BricxCC

Reasonably stable development environmentProvides support for all LEGO robotic platformsFree!

Programming with NXC

Assuming you are comfortable with C…

How to use the motorsHow to read the sensorsThreading model

NXC Programs

NXC is based on CRestrictions because it’s based on the built-in P-Code system There’s no stack Limited memory Limited number of tasks (256) And subroutines, which are also

‘tasks’

NXC program skeleton

#include "NXCDefs.h"

task main() { }

NXC Sensors

#include "NXCDefs.h"

task main() { SetSensorType( IN_1,

SENSOR_TYPE_TOUCH ); SetSensorMode( IN_1,

SENSOR_MODE_BOOL ); }

NXC Sensors

#include "NXCDefs.h"

task main() { SetSensor( IN_1, SENSOR_TOUCH ); }

NXC Sensors

To read a sensor use

x = Sensor( IN_1 );

NXC Sample program#include "NXCDefs.h“task main() { SetSensor( IN_1, SENSOR_TOUCH ); while( true ) { if( Sensor( IN_1 ) ) { PlayToneEx(440, 100, 3, false); TextOut( 0, LCD_LINE1, "TOUCHING!"); while( Sensor( IN_1 ) ) ; } TextOut( 0, LCD_LINE1, "---------"); while( !Sensor( IN_1 ) ) ; }}

NXC Motors

Simple motor commands are available OnFwd(), OnRev(), Off(), Float()

NXC Motors

To use the built-in rotation sensors, you need to use the new motor commandsEasiest to use is RotateMotor()

RotateMotor

RotateMotor( port, speed, angle ); port is OUT_A, OUT_B, OUT_C, or

combinations such as OUT_AB, OUT_ABC

speed is a number -100 to 100 angle is the number of degrees you

want the motor to turn (positive or negative)

Mimicking a Servo Motor

Read the current motor angle Current =

MotorRotationCount( OUT_A );

Calculate how far you need to turn Delta = Target – Current;

Turn that amount RotateMotor( OUT_A, speed, Delta );

Displaying Text

The LCD display is useful for Debugging Setting parameters Runtime messages Graphics Games … and more

Displaying Text

TextOut( x, y, text );NumOut( x, y, number );

LCD display

The origin is the bottom leftSo TextOut( 0,0, “hi” ) will display in the bottom left cornerUse the LCD_LINEn macros if you like to make it easier

Text Example

y = 42;TextOut(0, LCD_LINE5, "Answer:" );NumOut( 8*6, LCD_LINE5, y );

// characters are 6 pixels wide

Graphics

There are also commands to draw lines, circles, rectangles, and set pointsYou can display bitmaps from a fileRIC files – contain drawing commandsOne problem is there isn’t an easy way to clear areas of the screen It’s easy to clear the whole screen You can display a 1x1 blank bitmap

Tasks and Subroutines

Multiple tasks are possible, but don’t work like you might expectScheduling is different – tasks start when a ‘dependant’ task finishes There is no easy way of stopping a

task

Use Precedes() or Follows() in a task to define task dependencies

Taskstask FooTask() { // will start executing when main() finishes}

task main() { // program starts here Precedes( FooTask );}

task BarTask() { Follows( main ); // will also start executing when main()

finishes}

Subroutines

Essentially a task that can be calledIt suspends the calling task until it returnsDon’t use task keyword to define theseCan pass in parameters or return a value

Subroutine Examplevoid TestSub( int x, int y, short i ) { x = y + i; }task main() { TestSub( 1, 2, 3 ); }

NXC Help

Preliminary help file is a PDFThere are many samples and a tutorial online