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    ELE 574 Dr. Shadi Alboon2

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    What is C ?

    In 1970 a team at Bell Labs led by Brian Kernighan were

    developing the UNIX computer operating system

    They required a high-level computer language for writingcomputer operating systems

    Starting from an existing language called BCPL theydeveloped C

    C was used to write the next version of UNIX system

    software

    UNIX eventually became the world's first portableoperating system

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    Why Program PICs in C?

    C is a portable language, requiring minimal modificationwhen transferring programs from one processor to another

    Programming in a high-level language rather thanassembler allows programs to be developed much morerapidly

    Typically a program which takes a few weeks in assemblercan be written in C in a few days

    Code efficiency of compiled C programs is typically 80% of

    well-written assembler programs

    The related language C++ is too complex for use with thepresent generation of PICs

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    CCS PIC Compiler

    A compiler converts a high-level language program tomachine instructions for the target processor

    A cross-compiler is a compiler that runs on a processor

    (usually a PC) that is different from the target processor

    os em e e sys ems are now programme us ng eC/C++ language

    Several C compilers are available that target Microchip

    PICs, for example HiTech, Microchip and CCS The PIC programming laboratory at Reading is equipped

    with the CCS cross-compiler

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    CCS PIC Compiler

    Programs are edited and compiled to PIC machine instructions on a PC

    PIC machine instructions are uploaded from PC to PIC system via theICD2 debugger

    Code is executed on the PIC system and can be debugged (breakpoints inspect variables single points, variables, step etc.) using PC

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    CCS PIC Compiler

    The CCS compiler comes with an integral syntax-aware

    editor

    CCS C is standard C plus limited support for referenceparameters in functions

    PIC-specific pre-processor directives are provided in addition

    o e s an ar rec ves nc u e, e ne e c :#inline Implement the following function inline#priority set priority of interrupts

    Additional functions supporting PIC hardware are provided:

    output_low() set an I/O port bit low

    delay_us() delay by a specified number of s

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    CCS PIC Compiler Data Types

    PICs are optimized for processing single bitsor 8-bit words, and this is reflected the CCScompiler word sizes:

    Contrary to the C standard, CCS C integersare by default unsigned

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    CCS PIC Compiler Data Types

    In CCS C a short int is effectively a boolean variable

    To make programs more readable it is a helpful to makeuse of the definitions (already in the device definitionfiles):

    #define boolean short int

    #define false 0

    #define true 1

    Now it is possible to declare boolean variables:

    boolean finished = true;

    The standard boolean operators (||, &&, ! etc) can be

    used with these variablesELE 574 Dr. Shadi Alboon 9

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    Device Definition File

    A CCS C program pre-processor will start with a numberof directives similar to:

    #include #fuses HS,NOWDT,NOBROWNOUT,NOPROTECT,PUT

    #use delay(clock=20000000)

    " .

    The first directive instructs the compiler to include thesystem header file 18F452.H

    This is a device-specific file that contains informationabout the location of SFRs and the values to be writtento them

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    Fuses

    CCS C provides a fuse directive:

    #fuses HS,NOWDT,NOBROWNOUT,NOPROTECT,PUT

    which specifies the states of the configuration fuses thatshould be programmed onto the PIC

    n s examp e:

    HS Clock is a high-speed crystal or resonator

    NOWDT Watchdog timer is disabled

    NOBROWNOUT Brown-out detector is disabled

    NOPROTECT Code protect off

    PUT Power-on timer is enabled

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    Delays

    CCS C provides functions for generating delays:

    delay_us()

    delay_ms()

    These delay functions actually delay by a number ofmachine c cles

    The compiler needs to know the clock frequency in orderto calculate the required number of machine cycles

    #use delay(clock=20000000)

    This use-delay directive specifies that the clock

    frequency of the PIC is 20 MHz

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    Multiple Source Code Files

    CCS C does not allow separate compilation and linkingof source code files

    It is convenient (and good programming practice) to put

    commonly-used library functions in separate files

    " ".

    This directive instructs the compiler to include the userlibrary file lcd.c in the file currently being compiled

    This is not particularly efficient (the library file is compiled

    every time) - however typical PIC programs compile in afew seconds

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    CCS PICCCS PICProgramming ExamplesProgramming Examples

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    Program Blank

    #include "16F877A.h" // Specify PIC MCU

    #use // Include library routines

    void main() // Start main block

    int // Declare global variables

    while(1) // Start control loop

    {

    // Program statements}

    } // End main block

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    A basic set of CCS C components

    Compiler Directives

    #include source files Include another source code or header file#use functions(parameters) Include library functions

    C Blocks

    main(condition) {statements } Main program blockwhile(condition) {statements } Conditional loop

    for(condition) {statements } Preset loop

    C Functions

    delay_ms(nnn) Delay in milliseconds

    delay_us(nnn) Delay in microsecondsoutput_x(n) Output 8-bit code at Port Xoutput_high(PIN_nn) Set output bit highoutput_low(PIN_nn) Set output bit lowinput(PIN_nn) Get input

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    Integer Variables

    Name Type Min Max

    int1 1 bit 0 1

    unsigned int8 8 bits 0 255

    -

    unsigned int16 16 bits 0 65525

    signed int16 16 bits -32767 +32767

    unsigned int32 32 bits 0 4294967295

    signed int32 32 bits -2147483647

    +2147483647

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    Conditional Operators

    OperationSymbol

    EXAMPLE

    Equal to == if(a == 0) b=b+5;

    Not equal to != if(a != 1) b=b+4;

    Greater than > if(a > 2) b=b+3;

    Less than < if(a < 3) b=b+2;

    Greater than or equal to >= if(a >= 4) b=b+1;

    Less than or equal to

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    A program to output a binary code

    #include "16F877A.h" // MCU select

    void main() // Main block

    {

    output_D(255); // Switch on outputs}

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    RA0/AN02RA1/AN1

    3

    RA2/AN2/VREF-4

    RA4/T0CKI6

    RA5/AN4/SS7

    RE0/AN5/RD8

    OSC1/CLKIN13

    OSC2/CLKOUT14

    RC1/T1OSI/CCP2 16

    RC2/CCP1 17

    RB7/PGD 40

    RB6/PGC 39

    RB5 38RB4 37

    RB3/PGM 36

    RB2 35

    RB1 34

    RB0/INT 33

    RA3/AN3/VREF+5

    RC0/T1OSO/T1CKI 15

    MCLR/Vpp/THV1

    U1

    LED-BARGRAPH-

    REDRE1/AN6/WR

    RE2/AN7/CS

    10 RC3/SCK/SCL

    RD0/PSP0 19

    RD1/PSP1 20

    RD7/PSP7 30

    RD6/PSP6 29

    RD5/PSP5 28RD4/PSP4

    27RD3/PSP3

    22RD2/PSP2

    21

    RC7/RX/DT 26

    RC6/TX/CK 25

    RC5/SDO 24RC4/SDI/SDA

    23

    PIC16F877

    1

    23

    45

    67

    8

    20

    1918

    1716

    1514

    139 12

    10 11 2

    34

    56

    78

    9

    1

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    Variables : Outputs an 8-bit variable

    #include "16F877A.h"

    void main(){

    int x; // Declare variable and type

    =

    output_D(x); // Display the value in binary}

    The same circuit as before

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    Endless loop : Outputs variable count

    #include "16F877A.h"

    void main()

    {

    int x; // Declare variable

    while(1) // Loop endlessly

    { output_D(x); // Display value

    x++; // Increment value

    }

    }

    The same circuit as beforeELE 574

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    RA0/AN02

    RA1/AN13

    RA2/AN2/VREF-4

    RA4/T0CKI6

    RA5/AN4/SS7

    OSC1/CLKIN13

    OSC2/CLKOUT14

    16

    RB7/PGD 40

    RB6/PGC 39

    RB5 38

    RB4 37RB3/PGM 36

    RB2 35

    RB1 34

    RB0/INT 33

    RA3/AN3/VREF+5

    RC0/T1OSO/T1CKI 15

    MCLR/Vpp/THV1

    U1

    R110k

    test circuit with input switch

    RE0/AN5/RD8

    RE1/AN6/WR9

    RE2/AN7/CS10

    RC2/CCP1 17

    RC3/SCK/SCL 18

    RD0/PSP0 19

    RD1/PSP1 20

    RD7/PSP7 30

    RD6/PSP6 29

    RD5/PSP5 28

    RD4/PSP4 27RD3/PSP3 22

    RD2/PSP2 21

    RC7/RX/DT 26

    RC6/TX/CK 25

    RC5/SDO 24

    RC4/SDI/SDA 23

    PIC16F877

    D1

    LED-RED

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    IF statement: Tests an input

    #include "16F877A.h"

    void main()

    {

    int x; // Declare test var.

    ou pu _ ; ear a ou pu s

    while(1) // Loop always

    {

    x = input(PIN_C0); // Get input

    if(x==1)output_high(PIN_D0); // Change out}

    }

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    Conditional loop: Input controls outputloop

    (While loop)

    #include "16F877A.h"

    #use delay (clock=1000000) // MCU clock = 1MHz

    void main()

    {

    while(1)

    {

    while(input(PIN_C0)); // Repeat while switch open{ output_high(PIN_D0);

    delay_ms(300); // Delay 0.3s

    output_low(PIN_D0);

    delay_ms(500); // Delay 0.5s

    }output_low(PIN_D0); // Switch off LED

    }

    }

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    ELE 574 Dr. Shadi Alboon26


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