Shulou(Shulou.com)06/01 Report--

In the next few sections, we will take everyone to write the first single-chip microcomputer program. Before that, let's first understand some of the unique program syntax of 51 single-chip microcomputer and the basic operation pace of Keil software. Please be patient.

We mainly use C language to program the single-chip microcomputer, and some single-chip computers have a few very special unique programming statements, 51 single-chip microcomputer has, first introduce 2.

The first statement is: sfr P0 = 0x80

Sfr, the crux of the word, is unique to 51 single-chip microcomputer, his influence is to define a single-chip microcomputer special function memory (special function register). There are many small modules outside the 51 single-chip microcomputer, each module lives in a room with a unique room number, and each module has 8 master switches. P0 is a functional module, living in the 0x80 this room, we are by setting P0 external module of the 8 switches, to let the P0 of these 8 IO ports input high-level or low-level. And 51 single-chip microcomputer external there are many memory, if we want to use, then we must stop the sfr declaration early. However, Keil software has written all these statements afterwards and kept them in a special file. If we want to use them, we only need to add a line # include at the end of the file, which can be explained in more detail later.

The second statement is: sbit LED = P0 ^ 0

This sbit is a stop boundary for one of the eight switches in SFR. After the second sentence above, you only need to write LED in the program to represent P0.0 (the symbol "^" is on top of the number key 6). Note that P must be capitalized, that is to say, we have given P0.0 a more abstract name called LED.

After understanding these two sentences, let's take a look at the special function memory of the single-chip microcomputer. Please note that each model of MCU is equipped with a data manual (Datasheet) compiled by consumer manufacturers, so let's take a look at STC89C52's data manual, from page 21 to page 24, with an introduction to special function memory and an address mapping list. We must stop clarifying the address of the memory before we can use it. Is there too much colorful, can not remember, this does not matter, do not need you to remember, understand, after most of I will gradually explain to everyone, less local needs of the time, I used to check the manual, do skills is not for perfunctory tests, you can look through the manual to find the materials you need at any time.

Figure 2-7 is the table at the bottom of page 22 of the intercepted manual.

Figure 2-7 IO port special function memory

Let's take a look at this table, the expansion of P4 STC89C52 to specification 51, we first ignore it, only look at the front P0, P1, P2, P3 these four, each P port itself has 8 master ports. Everyone can combine our pioneering board truth diagram or figure 2-1, so it is certain that our single-chip microcomputer has a total of 32 IO ports (IO,Input and Output, distinguish between output and input).

The address of the P0 port is 0x80. There are 8 IO palms from 7 to 0, followed by a Reset Value (reset value). This is a very important parameter that we must see in the memory. Most of the 8 master bit reset values are 1.

This is to inform us that whenever the single-chip microcomputer power-on reset, the value of all the pins is mostly 1, that is, high level, we should also fully consider this achievement when designing the circuit.

So the above two sentences, when we write sfr, we must write according to this address (Add) in the manual. When we write sbit, we can directly take out a byte. When we are programming, there is also a ready-made header file that writes the address of the memory. We can just include the header file directly, and we don't need to write it one by one.

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