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 fourth part we will see how to read the digital state of a pin. This means reading if the pin is at 0 volts (low) or 3.3 volts (high).
For this example we will need a couple of extra parts:
- A breadboard
- An LED
- A 470 ohm resistor
- A push button
- A couple of wires to connect them all
We start from the same circuit as the part three example, and we add a push button.
To control the IO pin we are going to use the function
Set of the package
function Set (Pin : Pin_Id) return Boolean with Pre => Supports (Pin, Digital);
- Pin : The id of the pin that we want to read as digital input
- The procedure
Sethas a precondition that the pin must support digital IO.
As you can see, the function
Set to read the pin has the same name as the
set that we used to control the pin in the
output example. It is called overloading, two subprograms
with the same name that provide different services.
In the code, we are going to write an infinite loop that reads the state of pin
1. If it is high, it means the button is not pressed so we turn off the LED on pin
0. It if it is low, it means the button is pressed so we turn on the LED on pin
Here is the full code of the example:
with MicroBit.IOs; procedure Main is begin -- Loop forever loop -- Check if pin 1 is high if MicroBit.IOs.Set (1) then -- Turn off the LED connected to pin 0 MicroBit.IOs.Set (0, False); else -- Turn on the LED connected to pin 0 MicroBit.IOs.Set (0, True); end if; end loop; end Main;
Following the instructions of Part 1 you can open this example (Ada_Drivers_Library-master\examples\MicroBit\digital_in\digital_in.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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