Page 34 of 229 Start Back Next End ZBasic Language Reference 24 ZBasic Microcontrollers Only one-dimensioned arrays whose lower bound is 1 may be passed as parameters and they must be passed by reference. The upper bound is indeterminate – it is the responsibility of the programmer to ensure that the subroutine does not access elements beyond the upper bound of the passed array. Often, programmers will include a parameter that specifies the upper bound so that the code may safely operate with different sizes of arrays. Sub mySub(ByRef data() as Byte, ByVal count as Byte) End Sub Lastly, the <statements> element in the subroutine definition represents zero or more valid ZBasic statements that are described in Section 2.5 of this manual. Example Private Const redLED as Byte = 25 ' define the pin for the red LED Private Const grnLED as Byte = 26 ' define the pin for the green LED Public Sub Main() ' configure the pins to be outputs, LEDs off Call PutPin(redLed, zxOutputHigh) Call PutPin(grnLed, zxOutputHigh) ' alternately blink the LEDs Do ' turn on the red LED Call Blink(redLed) ' turn on the green LED Call Blink(grnLed) Loop End Sub Private Sub Blink(ByVal pin as Byte) ' turn on the LED connected to the specified pin for one half second Call PutPin(pin, zxOutputLow) Call Delay(0.5) Call PutPin(pin, zxOutputHigh) End Sub In this program, we have factored out the code that turns an LED on and off into a subroutine named Blink(). In the definition of Blink(), pin is called the formal parameter. In Main() where Blink() is invoked, the parameters redLed and grnLed are the actual parameters. By factoring out the code that was common to blinking the two LEDs we have simplified the program. The details of how an LED is blinked are encapsulated in the definition of Blink(). No longer does the Main() subroutine need to know how to blink an LED; it just calls the subroutine to handle all of the details of blinking an LED connected to a specific pin and provides the necessary data for Blink() to do the work. In this case, all that is needed is a pin number. If we wished to do so, we could add another parameter to the blink subroutine to specify how long we want the LED illuminated. Private Sub Blink(ByVal pin as Byte, ByVal duration as Single) ' turn on the LED connected to the specified pin for the time given Call PutPin(pin, zxOutputLow) Call Delay(duration) Call PutPin(pin, zxOutputHigh) End Sub With this definition, we would need to add a second actual parameter in each call. For example,