Three simple button-LED c-programs illustrating the use of macros.

Here are three simple programs in c for the AVR tiny44 that all do the same thing: turn on an LED when a button is pressed. Refer to the datasheet for the functions of register DDRx, PORTx, and PINx, where x=A,B. Refer to c programming introductions for the use of operators that work on bits.

There is an LED on pin PB2, physically pin 5 of the Tiny44.

There is a button on PA5.

The three programs:

1. Here is a simple program and makefile to light an LED in response to a button.

• button_44_a.c
• button_44_a.make

Comments:

• It's simple. You can tell that it is all done by putting numbers into registers and checking values of registers.
• But, to see what is going on, you need to count bits and keep track of numbers. It's easy to make mistakes.
• If you need to change pins, or alter the program for another board arrangement, you have to change numbers in several places.
• It can get very confusing if you are doing anything more complex.

2. Here is a clearer way to do it, using macros.

• button_44_b.c
• button_44_b.make

Comments:

• It reads more like spoken language. Once you are comfortable with operations on bits of bytes, it is clearer than the first one.
• If you want to change pins, you still have to change numbers in several places, and remember for more than a second or two where you put things.
• If you wanted to change input or output to a different port, you would have to make several changes in the main function and keep track of them.

3. Here's another way to use macros to do the same thing.

• button_44_c.c
• button_44_c.make

Comments:

• Again, it reads like English. It has more levels of definitions and seems more complex.
• But, if you want to change or add pins, the change is done once, in the #define macros. No changes need to be done within the main function.
• There is no confusion, for example, if input and output are done on different pins of the same port.