Ada for micro:bit Part 3: Pin Output

by Fabien Chouteau – Sep 29, 2020

Welcome to the Ada for micro:bit series where we look at simple examples to learn how to program the BBC micro:bit with Ada.

If you haven't already, please follow the instructions in Part 1 to setup your development environment.

In this third part we will see how to control the output state of a micro:bit pin by lighting an LED.

Wiring Diagram

For this example we will need a couple of extra parts:

A breadboard
An LED
A 470 ohm resistor
A couple of wires to connect them all

Wiring the LED directly from the output pin to ground will make it burn, so we have to add a resistor to limit the flow of current.

Interface

To control the IO pin we are going to use the procedure Set of the package MicroBit.IOs.

procedure Set (Pin : Pin_Id; Value : Boolean)
  with Pre => Supports (Pin, Digital);

Arguments:

Pin : The id of the pin that we want to control as digital output
Value : A Boolean that says if we want the pin to be high (True) or low (False)

Precondition:

The procedure Set has a precondition that the pin must support digital IO.

We also use the procedure Delay_Ms of the package MicroBit.Time to stop the program for a short amount of time.

Here is the full code of the example:

with MicroBit.IOs;
with MicroBit.Time;

procedure Main is
begin

   --  Loop forever
   loop
      --  Turn on the LED connected to pin 0
      MicroBit.IOs.Set (0, True);

      --  Wait 500 milliseconds
      MicroBit.Time.Delay_Ms (500);

      --  Turn off the LED connected to pin 0
      MicroBit.IOs.Set (0, False);

      --  Wait 500 milliseconds
      MicroBit.Time.Delay_Ms (500);
   end loop;
end Main;

Following the instructions of Part 1 you can open this example (Ada_Drivers_Library-master\examples\MicroBit\digital_out\digital_out.gpr), compile and program it on your micro:bit.

See you next week for another Ada project on the micro:bit.

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About Fabien Chouteau

Fabien joined AdaCore in 2010 after his engineering degree at the EPITA (Paris). He is involved in real-time, embedded and hardware simulation technology. Maker/DIYer in his spare time, his projects include electronics, music and woodworking.