Label, Jump, Return and Subroutine

The Label and Jump commands are used together to create loops and make decisions.

Subroutines can be created using the Subroutine, Jump and Return commands together.

Using labels and jumps

You can use the Label command to give a line its own unique name — in this example the line’s name is Start:

Label Start

You can then refer to this label by name in a Jump command, anywhere else in a sequence:

Jump To Start

Creating loops

This simple loop will play forever, flashing the LED named Status on and off every second. When the Jump command is played, MECControl jumps to the line labelled Start and continues playing the sequence from there:

Label Start

Light Status
Wait 1 Second
Light Status Black
Wait 1 Second

Jump To Start

You can add a condition to a Jump command, so that the jump only occurs if the condition is met.

In this loop, the Status LED will flash until the Pressed action of a Button named StopButton occurs:

Label Start

Light Status
Wait 1 Second
Light Status Black
Wait 1 Second

Jump To Start Until StopButton Pressed

You can create loops that play a set number of times by testing the number stored inside a variable.

In this loop, the Status LED will flash five times:

Let Counter = 0

Label Start

Light Status
Wait 1 Second
Light Status Black
Wait 1 Second

Let Counter = Counter + 1

Jump To Start Until Counter = 5

Using symbols other than Equal ( = ) you can perform other tests on the number stored inside a variable:

Less Than ( < )
Less Than or Equal ( <= )
Not Equal ( <> )
Greater Than or Equal ( >= )
Greater Than ( > )

Making decisions

In this example, a Motor named Jib will run Clockwise if the Pressed action of a Button named RaiseJibButton occurs, or Counterclockwise if the Pressed action of a Button named LowerJibButton occurs:

Label Start

Jump To RaiseJib If RaiseJibButton Pressed
Jump To LowerJib If LowerJibButton Pressed

Jump To Start

Label RaiseJib
Run Jib Clockwise
Jump To Start

Label LowerJib
Run Jib Counterclockwise
Jump To Start

If you use a Wait command to wait for a Keypress, you can a make decisions based on the Key that was Pressed, as in this re-working of the previous example::

Label Start

Wait For Keypress
Jump To RaiseJib If Up Key Pressed
Jump To LowerJib If Down Key Pressed

Jump To Start

Label RaiseJib
Run Jib Clockwise
Jump To Start

Label LowerJib
Run Jib Counterclockwise
Jump To Start

Now the Jib motor will run Clockwise if you press the Up cursor key, and Counterclockwise if you press the Down cursor key. You can test to see if any of the following keys have been pressed:

Apostrophe or '
Asterisk or *
Backslash or \
Backspace
Comma or ,
Cursor Up, Down, Left or Right
Delete
Digits 0 to 9
End
Enter or Return
Equals or =
FullStop, Period or .
GraveAccent or `
Hash, Pound or #
Home
Hyphen or -
Insert
LeftSquareBracket or [
Letters A to Z
Minus
PageDown
PageUp
Plus or +
RightSquareBracket or ]
Semicolon or ;
Slash or /
Space
Tab

You can also test to see if any key has been pressed, or no key has been pressed:

Jump To RaiseJib If Any Key Pressed
Jump To LowerJib If No Key Pressed

You can also access a property of a device and use it to make a decision, as in this example:

Jump To Start If Arm Position > 45 Degrees

Here the jump to the Start label will occur only if the Position property of a Meccanoid Servo Motor named Arm is greater than 45 degrees clockwise.

Creating subroutines

If you find yourself writing the same list of commands over-and-over, you could instead create a subroutine containing those commands. Here is the flashing LED loop example, re-written as a subroutine:

Subroutine FlashStatusLED

Let Counter = 0

Label Start

Light Status
Wait 1 Second
Light Status Black
Wait 1 Second

Let Counter = Counter + 1

Jump To Start Until Counter = 5

Return From Subroutine

Notice the addition of the FlashStatusLED Subroutine label, which gives the subroutine a name, and the Return command. These allow you to use to access the subroutine from anywhere else in the sequence, as in this example:

Jump To FlashStatusLED
Wait 10 Seconds

Jump To FlashStatusLED
Wait 10 Seconds

Jump To FlashStatusLED
Wait 10 Seconds

Here the subroutine runs three times, separated by 10 second pauses.

Whenever the Return command inside the subroutine is played, MECControl returns to the line after the last Jump command and continues playing the sequence from there.