The learning journey of a MCU beginner (Part 7) --- Dynamic display of digital tubes

In the previous article, we talked about using 74LS138 to control the bit selection of digital tubes. How to select it? Let's take a look at the manual of this decoder.

74LS138

/Y0--/Y7 is data output

A0--A2 is data input

/E1, /E2, E3 are enable controls, /E1 and /E2 are low level effective, E3 is high level effective

VDD is connected to the power supply; GND is connected to the ground

The most important thing is the truth table, to explain how it works

/E1 and /E2 are low level valid, E3 is high level valid, as long as one of them does not meet the conditions, /Y0--/Y7 will all output high level, our common cathode digital tube will not light up

All are satisfied from the fourth row onwards, and now you can look at A0--A2, the order is A2-

A1-A0, from top to bottom, are 000, 001, 010, 011, 100, 101, 110, 111. This shows that they are binary 0, 1, 2, 3, 4, 5, 6, 7. Look at the right half of Y0, 000 is Y0, 001 is Y1, 010 is Y2... Once you correspond, you will know how it is controlled?

Code:

Digital tube dynamics

There is a switch statement switch(i) which judges i. When i is 0, the statements after case 0 are executed. Add a break after each statement, otherwise the following statements will be executed continuously.

A for loop realizes the requirement that different digital tubes display different numbers. When i is 0, the first digital tube lights up and the number is 0. When i is 1, the second digital tube lights up and displays the number 1.

P0 = 0x00 is to make the P0 port more stable and return to its original position

I suddenly had an idea halfway through writing, which made it more difficult. I had to display it once and then do it again in reverse.

Improve

In fact, a nested for loop is added, which is judged as follows...

That 9 took a lot of time. I kept writing 8, so the display was 0, 1, 2, 3, 4, 5, 6, 0, 7, 6, 5, 4, 3, 2, 1, 0

I thought a and i were synchronized. I was careless and my foundation was not solid. a is in the order of 1, 2, 3, 4, 5, 6, 7... So when i is 7, a is 8, so here I write <9

The case 4 is protruding out of hand because of carelessness, but this is C language so the indentation is not a problem. If it is Python that relies on indentation for positioning, there will be a problem, but it seems that Python is rarely used to write microcontrollers. . . .

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