PIC microcontroller C language programming (15)

　　This article is the concluding chapter of the lecture "Microcontroller C Language Programming". In order to help everyone better master the knowledge learned previously, we will summarize the thinking methods and basic knowledge that beginners should have when editing PIC microcontroller utilities with C language, and summarize it through the following examples, in order to help everyone to further study PIC microcontroller C language programming in the future.

　　16. Composition of PIC microcontroller C language program

　　A complete PIC microcontroller C language source program should include: header file, variable definition, constant description, function definition, main function main(), several other function functions, various functional C statements, as well as defined functions and function bodies, comments and other parts.

　　Note: For intermediate or lower-level PIC microcontrollers, the header files are #include and #include; for advanced products, such as the PIC18F452 device, the header files are #include and #include< pic18fxx2.h>.

　　The operation of a C program always starts from the main function main() (which can be directly observed through simulation), and the main function calls other functions, and other functions can also call each other, and the operation works in this way. C statements can be divided into sequential structures, selection structures, and loop structures according to their different execution methods. The sequential structure here means that the program executes one by one in the order of statements; the selection structure refers to the execution order selected by the program according to relevant conditions; the loop structure means that the program executes a section of the program according to the existence of a certain condition until the condition disappears. If the condition always exists, an infinite loop is formed.

　　1. Three expressions of delay function

　　When editing a large PIC microcontroller program in assembly language, it is generally divided into multiple program modules, and the subroutine of each module implements a specific function. When editing the program in C language, the function of the module is implemented by function, that is, the function is equivalent to the subroutine of assembly language. Below we use the example of delay function application to illustrate the basic composition format of PIC microcontroller C language program.

　　The delay function is a function that appears frequently in the source program of the PIC microcontroller, and there are many forms of delay functions with the same function. We choose three commonly used delay functions for discussion.

　　The three delay functions cited are all implemented by loop control statements - while, do_while and for.

　　(1) A delay function consisting of a for statement with formal parameters.

　　void delay(unsigned int k)

　　{

　　unsigned int i, j;

　　fir（i=0;i<=81;i++）

　　fir（j=0;j<=k;j++）

　　cONtinue;

　　}

　　The delay function consists of two for statements. The 81 in the first for statement is a constant set by the author (can be set arbitrarily) to increase the delay value; the k in the second for statement is the value given by the user when the main function main() calls delay(k) in the program. Different k values ​​will result in different delay times. Therefore, the delay function can implement multiple different delay amounts in a C program, which is obviously much simpler than the assembly language delay subroutine. When the delay amount is required to be shorter, the functions of the two for statements in the delay function can be implemented with one for statement.

　　(2) A delay function consisting of a while loop statement with formal parameters.

　　Void deley(unsigned long int k)

　　{

　　Unsigned long int d=k;

　　While (--d)

　　{;

　　}

　　{

　　This delay function is simple and easy to remember. When in use, when the main function main() in the program calls delay(k), the user can give different k values ​​to achieve multiple delay values.

　　(3) A delay function consisting of a do-while statement with formal parameters.

　　Void delay(unsigned long int k)

　　{

　　Unsigned int long j=o;

　　do {

　　j++;

　　}

　　While (j <= k);

　　j=o;

　　}

　　This delay function is simple and easy to remember. When using it, when the main function main() in the program calls delay(k), the user can give different k values ​​to achieve multiple delay values.

　　It should be noted that the formal parameters in the delay function composed of the while loop statement and the do-while statement above do not necessarily use long integers (long ink).

　　⒉ Four C programs with the same circuit function but different forms

　　The following describes how to use the 8 LEDs connected to the PORTB port of the PIC16F84A microcontroller and use four C programs to control the LED lights of the port to illustrate the basic format and flexibility of editing C language programs. The circuit is shown in Figure 1 in the article "Microcontroller C Language Programming (1)" in the 9th issue of "Electronic Production" in 2009. The program flow is shown in Figure 64, which uses an infinite loop working mode.

Fig.64

　　(1) C program 1, file name is pic09.c, the listing is as follows:

　　#include // header file

　　void delay(unsigned long int K)

　　// Delay function starts

　　{

　　unsigned int long j=0;

　　// Explanation statement

　　do

　　// Delayed execution statement composed of do-while

　　{

　　j++;

　　}

　　while(j<=K);

　　j=0;

　　}

　　main() // Start of main function

　　{

　　TRISB=0x00;

　　// Set PORTB to output

　　INTCON=0x00; // Disable all interrupts

　　PORTB=0x00; //RB port sends low level first

　　while（1） // Start of a permanent loop

　　{

　　PORTB=0x55;

　　//RB port externally connects LEDs 1, 3, 5, and 7 to light up

　　delay(45000);

　　// The lit LED will be turned off after 1 second delay

　　PORTB=0xAA;

　　//RB port externally connects LEDs 2, 4, 6, and 8 to light up

　　delay(98000);

　　// The lit LED turns off after a delay of 2 seconds

　　PORTB=0xFF; //RB port external LED all lights up

　　delay(155000);

　　// All LEDs will turn off after 3 seconds

　　}

　　}[page]

Note: a. In the above program, the delay function has a formal parameter K and consists of a do-while statement.

　　b. When the main function main() calls delay(k), its K is 45000 (1 second), 98000 (2 seconds), and 155000 (3 seconds).

　　c. The infinite loop when the LED light is on is completed by the while (1) statement.

　　(2) C program 2, file name is pic10.c, the listing is as follows:

　　#include // header file

　　void delay（ K ） // delay function

　　unsigned long int K;

　　// Shape parameter (k) Description

　　{

　　unsigned long int d=K;

　　// Explanation statement

　　while (--d)

　　// Delayed execution statement composed of while

　　{;

　　}

　　}

　　main() // Start of main function

　　{

　　TRISB=0x00

　　// Set PORTB to output

　　INTCON=0x00; // Disable all interrupts

　　PORTB=0x00; //RB port sends low level first

　　loop: // statement label (infinite loop)

　　PORTB=0x55;

　　//RB port externally connects LEDs 1, 3, 5, and 7 to light up

　　delay(37000);

　　// The lit LED will be turned off after 1 second delay

　　PORTB=0xAA;

　　//RB port externally connects LEDs 2, 4, 6, and 8 to light up

　　delay(74000);

　　// The lit LED turns off after a delay of 2 seconds

　　PORTB=0xFF; //RB port external LED all lights up

　　delay(111000);

　　// All LEDs will turn off after 3 seconds

　　goto loop; // Jump to loop

　　}

　　Note: a. In the above program, the delay function has a parameter k and consists of a while statement.

　　b. When the main function main() calls delay(k), k is 37000 (1 second), 74000 (2 seconds) and 1110000 (3 seconds) respectively.

　　c. The infinite loop when the LED lights up is completed by the goto unconditional transfer execution statement. Where loop is the statement label. Be cautious when using the goto statement. It is necessary to use the goto statement in a simple C program, but editing a complex C program structure will make the program less readable.

　　(3) C program 3, file name is pic11.c, the listing is as follows:

　　#include // header file

　　unsigned int h; // unsigned integer variable

　　void delay(unsigned long int M)

　　// Delay function starts

　　{

　　unsigned int long i,j; // description statement

　　for（i=0;i<=81;i++）

　　// Consists of two for statements

　　for（j=0;j<=M;j++） // Delayed execution statement

　　continue; // continue the loop

　　}

　　main() // Start of main function

　　{

　　TRISB=0x00;

　　// Set PORTB to output

　　INTCON=0x00; // Disable all interrupts

　　PORTB=0x00; //RB port sends low level first

　　h=0; // assign 0 to h

　　do

　　// do-while statement starts the loop

　　{

　　PORTB=0x55;

　　//RB port externally connects LEDs 1, 3, 5, and 7 to light up

　　delay(500);

　　// The lit LED will be turned off after 1 second delay

　　PORTB=0xAA;

　　//RB port externally connects LEDs 2, 4, 6, and 8 to light up

　　delay(1000);

　　// The lit LED turns off after a delay of 2 seconds

　　PORTB=0xFF; // RB port external LEDs are all on

　　delay(1500);

　　// All LEDs will turn off after 3 seconds

　　h++; // h increments

　　}

　　while（h<=100）； //h increments when the condition is not met

　　h=0; // assign 0 to h

　　return; // return

　　}

　　Note: a. In the above program, the delay function has a shape parameter M and consists of two for statements (it can be multiple for statements or one for statement).

　　b. When the main function main() calls delay(M), the values ​​of M are 500 (1 second), 1000 (2 seconds) and 1500 (3 seconds).

　　c. The infinite loop when the LED light is on is completed by the do_while statement, and the 100 in while (h <= 100) can be any value greater than 0.

　　(4) C program 4, file name pic12.c, listing is as follows:

　　#include // header file

　　void delay(unsigned long int M)

　　// Delay function starts

　　{

　　unsigned int long j; // Explanation statement

　　for（j=0;j<=M;j++）

　　// A delay statement consisting of a for statement

　　continue; //For condition is met and the loop continues

　　}

　　void light1() ;

　　//Declare RB port LED light function 1

　　void light2() ；

　　//Declare RB port LED light function 2

　　void light3() ；

　　//Declare RB port LED light function 3

　　main() // Start of main function

　　{

　　TRISB=0x00;

　　// Set PORTB to output

　　INTCON=0x00; // Disable all interrupts

　　PORTB=0x00; //RB port sends low level first

　　while（1） // Start of a permanent loop

　　{

　　light1(); // Call LED light function

　　delay(45000); //Call the delay function (1 second)

　　light2(); //Call LED light function 2

　　delay(95000); //Call the delay function (2 seconds)

　　light3(); //Call LED light function 3

　　delay(145000); //Call the delay function (3 seconds)

　　}

　　}

　　void light1（ ） //LED light function 1

　　{

　　PORTB=0x55;

　　// RB port externally connected LEDs 1, 3, 5, 7 light up

　　}

　　void light2（ ） //LED light function 2

　　{

　　PORTB=0xAA;

　　//RB port externally connects LEDs 2, 4, 6, and 8 to light up

　　}

　　void light3（ ） //LED light function 3

　　{

　　PORTB=0xFF; //RB port external LED all lights up

　　}

[page]

Note: a. In the above program, the delay function has a parameter M and consists of a for statement.

　　b. When the main function main() calls delay(M), the M values ​​are 45000 (1 second), 95000 (2 seconds) and 145000 (3 seconds) respectively.

　　c. The infinite loop when the LED light is on is completed by the while statement.

　　d. The above programs are all completed with the LED function light1(); light2(); light3(). When the program is running, the main function main() calls the function and delay function of each LED. This method is necessary for editing complex C programs.

　　3. PIC microcontroller port bit definition

　　PIC microcontroller is a series of products, and the number of ports and the port bits are related to the specific model. For example, the ports of PIC16F877 are PORTA ~ PORTE, and the port bits are not all 8 bits. Its PORTA port has only 6 bits (RAO ~ RA5), and PORTAB, BORTC and PORTD are 8 bits, RB0 ~ RB7, RC0 ~ RC7, RD0 ~ RD7 respectively. When editing a C program, to access a certain bit of the above ports, you must first determine the address of this bit, which can be achieved through the @add (address) structure and the bit keyword, where @ is the address identifier and add (address) is the absolute address. Using the above address symbols, you can define the bits of the PIC microcontroller port, and then you can access the port bits at will. The following is a statement to define the bit of the PORTB port of PIC16F84A:

　　# dafine PORTBIT (add, bit) ((unsigned)

　　(&add)*8+(bit))

　　Satic bit PORTB_0@PORTBIT（PORTB,0）；//define bit 0 of PORTB

　　Satic bit PORTB_1@PORTBIT（PORTB,1）//define 1 bit of PORTB

　　…

　　Static bit PORTB_7@PORTBIT（PORTB,7）；//define PORTB bit 7

　　The "&" and "*" symbols are used as bitwise operators in C language, and 8 refers to 8 bits. When editing a PIC microcontroller C program, once a port, such as PORTB, is defined, its corresponding bit can also be written as RBO, RB1, RB2, RB3...RB7 to simplify the program code.

　　For the application of port bit definition, you can also refer to the program pic06.c in the article "Microcontroller C Language Programming (6)".

　　4. Application of LED digital display function

　　The following is a countdown and countdown C program example to illustrate the application of the LED digital display function display (x).

　　(1) Hardware circuit Use the PIC16F84A 4-digit LED digital display circuit (see Figure 3 and Figure 4 in the article "Microcontroller C Language Programming (4)") to make a 2-digit digital tube (the other two digits are not used) 99 to 0 countdown and countdown display. The countdown is in seconds and the countdown is in minutes. As long as there is a display function display(), the format of the counting and timing program is the same.

　　(2) The C source code listing for 99 to 0 (in minutes) is as follows. The program name is pic13.c.

　　#include // header file

　　#define PORTAIT (add, bit) ((unsigned)

　　(&add)*8+(bit))

　　static bit PORT_2@PORTAIT (PORTA, 2);

　　//PORTA port definition

　　static bit PORT_3 @PORTAIT(PORTA,3);

　　static bit PORT_4 @PORTAIT(PORTA,4);

　　unsigned int x=0; // unsigned integer variable

　　void delay(unsigned long int k)

　　// Delay function starts

　　{

　　unsigned long int i; // description statement

　　for（i=0;i<=k;i++） //for execution statement

　　continue; // continue the loop

　　}

　　void display(unsigned int x)

　　// Digital tube LED display function

　　{

　　unsigned int d=5700,unit_bit,ten_bit;

　　// Unsigned integer variable D, ones and tens

　　unsigned char SEG7[10]={0xc0,0xf9,0xa4,

　　//7-segment code array from 0 to 9

　　0xb0,0x99,0x92,0x82,0xf8,0x80,0x90};

　　unit_bit=x%10; // PICC can recognize single digits

　　ten_bit=x/10%10; //picc can recognize ten digits

　　while（d>0） //while statement starts

　　{

　　PORTA=0x1F;

　　//PORTA port low output high level

　　PORTB=SEG7[unit_bit];

　　// Send the bit field code array to port B

　　RA3=0; //RA3 is assigned a value of 0, and the LED displays the unit digit

　　delay（200）； // Delay for observation

　　RA3=1; //RA3 is assigned a value of 1, the LED unit digit is off

　　delay（2）； // short delay

　　PORTB=SEG7[ten_bit];

　　// Send the 10-bit field code array to port B

　　RA2=0; //RA2 is assigned a value of 0, and the LED displays the tens digit

　　delay（200）； // Delay to observe

　　RA2=1; //RA2 is assigned a value of 1, the LED tens digit is off

　　delay（2）； // short delay

　　d--; //d self-decrement

　　}

　　}

　　void main() // Main function starts

　　{

　　TRISB=0x00; //Port B is all output

　　TRISA=0x10; //The lower 4 bits of port A are output

　　PORTB=0x40; // Output 0 to the low bit of port B

　　INTCON=0x00; // Disable all interrupts

　　PORTA=0x10; //Port A low bit output 0

　　x=99; // Assign the value 99 to the integer variable x

　　while (RA4) // Display start signal

　　{; //RA4 is 0, timing starts

　　}

　　while（1） // while loop statement starts

　　{

　　display(x); // Call the display function

　　x--; //x decreases

　　if（x==-1） // if x is decremented to -1

　　x=99; // assign 99 to x

　　}

　　}

　　Note: a. For the above C source program, you only need to change the unsigned integer variable d (unsignedint d) in the display function display(x) from 5700 to 95 to turn it into a countdown program from 99 to 0 in seconds, because the value of d determines the time of the unit digit displayed by the digital tube (it is unique).

　　b. If you want to use the above program and have strict requirements on the timing (minutes or seconds) accuracy, you can fine-tune the integer variable d value (57000) based on the standard clock to achieve high-precision minute or second timing.

　　c. All the C source programs of the above PIC microcontrollers are executable and can be used by beginners without any worries.

　　5. Questions about PIC microcontroller C language program SIM software simulation

　　In "Single-Chip Microcomputer C Language Programming (11)" and "Single-Chip Microcomputer C Language Programming (12)", the SIM software simulation process of C programs is introduced in detail. Software simulation is very useful for beginners to edit PIC single-chip microcomputer C language programs. It can not only observe the program running process, but also find problems in the program. Even professionals who have mastered PIC programming technology often use SIM software simulation to find problems in the program.

　　Conclusion

　　The three expressions of delay function, four C programs with the same circuit function but different forms, port bit definition, LED digital display function and C language program SIM software simulation problems introduced above are all basic knowledge for beginners to edit source programs in C language for PIC microcontrollers. You should understand the content and remember and recite it. On this basis, you should also think of some simple circuit functions independently and complete them in C language for PIC microcontrollers (must be a successfully compiled executable program). After that, you can further learn operators, structures, unions, A/D conversion, serial communication and other contents in C language. When learning, you should still aim to edit executable utilities.