Microcontroller Principles

Although this logic function could have been implemented easier and cheaper in hard-wired (gate) logic, the purpose is to get students to think of performing logical operations by a sequenced set of instructions inside a programmable device (the MCU). This is a conceptual leap, basic but very important.

In case you’re wondering why I write in pseudocode, here are a few reasons:

No prior experience with programming required to understand pseudocode

It never goes out of style

Hardware independent

No syntax errors

If I had decided to showcase code that would actually run in a microcontroller, I would be dooming the question to obsolescence. This way, I can communicate the spirit of the program without being chained to an actual programming standard. The only drawback is that students will have to translate my pseudocode to real code that will actually run on their particular MCU hardware, but that is a problem guaranteed for some regardless of which real programming language I would choose.

Of course, I could have taken the Donald Knuth approach and invented my own (imaginary) hardware and instruction set . . .

The root of this question is little more than binary-to-hexadecimal conversion, but it also introduces students to the concept of controlling bit states in microcomputer ports by writing hex values. As such, this question is very practical! Although it is unlikely that someone would omit BCD-to-7-segment decoders when building a two-digit decimal display (because doing it this way uses so many more precious microcontroller I/O pins), it is certainly possible! There are many applications other than this where you need to get the microcontroller to output a certain combination of high and low states, and the fastest way to program this is to output hex values to the ports.

In case students ask, let them know that a dollar sign prefix is sometimes used to denote a hexadecimal number. Other times, the prefix 0x is used (e.g., $F3 and 0xF3 mean the same thing).