The fifth experiment - learn to do addition, subtraction, multiplication and division with me

Seeing this topic, haha, many people may want to hit Shitou brother with the board; what is 7+5? Do I need you to teach me this? But in the single-chip microcomputer, numbers are represented by binary: this is a bit difficult to understand/ Although our textbook has reached this point, you may not have learned a single instruction. But what I mean is to do a few experiments first to increase everyone's interest in single-chip microcomputers. There are too many specific instructions, but fortunately, generally we only need to remember 10-20 commonly used ones. OK, now start.

We write the following two instructions

MOV P1,#23H
END

I think everyone can understand this program. It sends the hexadecimal number 23H to the P1 port (i.e. P1.0--P1.7), compiles the HEX code and burns it, then inserts the chip into the experimental card holder; you can see that the status of P1.0-1.7 is;

P1.0 Off

P1.1 off

P1.2 Bright

P1.3 Bright

P1.4 Bright

P1.5 off

P1.6 Bright

P1.7 Bright

(Photo of Yitian Development Kit in action)

Why is this happening?

Note that because the 8 lights of our P1 port are connected to positive 5V at one end and the port at the other end, the port is low level 0. The LED is on. High level is not on. Arranged from high to low (from 1.7 to 1.0), it is 00100011. This number is 23H. What? You don't believe it? Well, please continue reading! 00100011 is 100011 in binary. According to the principle of mathematics, the leading 0 does not count.

Follow me to open the computer's Programs/Accessories/Calculator, and then set the calculator to scientific type. Then click Binary and enter 100011

Then click on the hexadecimal number and you can see that the number becomes 23. This is the 23H we entered.

Exercise: 25H+36H?

The procedure is as follows:

MOV R0,#25H; Send the immediate value 25 to register R0

MOV A,#36H; Send the immediate value 36 to accumulator A

ADD A,R0; add the contents of R0 and A, and the result is in A

NOP; no operation

POV P1,A; send the value of accumulator A to port P1.

END; End

After compiling the program, burn it into the chip and run it; you can see that the status of the light is

P1.0 Off

P1.1 off

P1.2 Bright

P1.3 Extinction

P1.4 Extinction

P1.5 Bright

P1.6 Extinction

P1.7 Bright

That is the binary number 01011011. Let's use the calculator above to see if the result is correct: first set the calculator to hexadecimal, enter 25+36 = the result is 5E

Then click on the binary result, which is 1011110. It can be seen that the result is completely correct.

You can then practice on your own

Subtraction instruction SUBB

Multiplication instruction MUL

Division instruction DIV

I believe that after learning this section, everyone will have a deep impression of these instructions. At the same time, it also gives us a better understanding of computer numbers.

Deep understanding.