chapter four transparency

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Chapter 4 C Language Programming
The 68HC11 Microcontroller
Han-Way Huang
Minnesota State University, Mankato
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• Introduction to C
• - C has gradually replaced assembly language in
  many embedded applications.
• A summary of C language constructs that will be
  used in 68HC11 programming.
• Books on C language
• 1. Kernighan Ritchie, The C Programming
  Language, Prentice Hall, 1988.
• 2. Deitel Deitel, C How to Program,
  Prentice Hall, 1998.
• 3. Kelly Pohl, A Book on C Programming in
  C, Addison-Wesley, 1998.
• A C program consists of functions and
  variables.
• A function contains statements that specify the
  operations to be performed.
• Types of statements
• 1. Declaration
• 2. Assignment
• 3. Function call
• 4. Control
• 5. Null
• A variable stores a value to be used during the
  computation.

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• A C Program Example
• include ltstdio.hgt -- causes the file
  stdio.h to be included
• / this is where program execution begins /
  -- a comment
• main () -- program execution begins
• -- marks the start of the program
• int a, b, c -- declares three integer
  variables a, b, and c
• a 3 -- assigns 3 to variable a
• b 5 -- assigns 5 to variable b
• c a b -- assigns the sum of a and
  b to variable c
• printf ( a b d\n, c) -- prints
  the string a b followed by value of c
• return 0 -- returns 0 to the caller
  of main( )
• -- ends the main( ) function
• Types, Operators, and Expressions
• - variables must be declared before they can be
  used.
• - A variable declaration must include the name
  and type of the variable and may
• optionally provide its initial value.

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- The name of a variable consists of letters and
digits. - The underscore character _ can be
used to improve readability of long variables. D
ata Types - C has four basic data types char,
int, float, and double.
- A variable of type char can hold a
single byte of data. - A variable of type int is
an integer that is the natural size for a
particular machine. - The type float refers to a
32-bit single-precision floating-point
number. - The type double refers to a 64-bit
double-precision floating-point
number. - Qualifiers short and long can be
applied to integers. For ImageCraft C
compiler, short is 16 bits and long is 32
bits. - Qualifiers signed and unsigned may be
applied to data types char and integer. Declarati
ons - A declaration specifies a type, and
contains a list of one or more variables of that
type.
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Examples of declarations int i, j, k char
cx, cy int m 0 char echo y / the
ASCII code of letter y is assigned to variable
echo. Constants - There are four kinds of
constants integers, characters, floating-point
numbers, and strings. - A character constant is
written as one character within single quotes,
such as x. A character constant is represented
by the ASCII code of the character. - A string
constant is a sequence of zero or more characters
surrounded by double quotes, as 68HC11 is made
by Motorola or , which represented an
empty string. Each individual character in the
string is represented by its ASCII code. - An
integer constant like 1234 is an int. A long
constant is written with a terminal l or L, as
in 44332211L.
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- A number in C can be specified in different
bases. The method to specify the base of a
number is to add a prefix to the number
Arithmetic Operators add and unary
plus - subtract and unary minus
multiply / divide -- truncate quotient to
integer when both operands are integers.
modulus (or remainder) -- cannot be
applied to float or double increment (by
1) -- decrement (by 1)
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Bitwise Operators - C provides six operators for
bit manipulations they may only be applied
to integral operands. AND OR XOR NOT
gtgt right shift ltlt left shift - is often
used to clear one or more bits of an integral
variable to 0. PORTD PORTD 0xBD / clears
bit 6 and bit 1 of PORTD to 0 / / PORTD is
of type char / - is often used to set one or
more bits to 1. PORTB PORTB 0x40 / sets
bit 6 to 1 (PORTB is of type char) / - can be
used to toggle a bit. abc abc 0xF0 /
toggles upper four bits (abc is of type
char) /
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- gtgt can be used to shift the involved operand to
the right for the specified number of
places. xyz xyz gtgt 3 -- shift right 3
places - ltlt can be used to shift the involved
operand to the left for the specified number of
places. xyz xyz ltlt 4 -- shift left 4
places - The assignment operator is often
combined with the operator. For example, PORTD
0xBD PORTB 0x40 xyz gtgt 3 xyz ltlt 4
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Relational and Logical Operators - Relational
operators are used in expressions to compare the
values of two operands. - The value of the
expression is 1 when the result of comparison is
true. Otherwise, the value of the expression is
0. - Relational and logical operators equal
to ! not equal to gt greater than gt greater
than or equal to lt less than lt less than or
equal to and or ! not (ones complement)
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Examples of Relational and Logical
Operators if (!(ADCTL 0x80) statement1 /
if bit 7 is 0, then execute statement1 / if (i
lt 10 i gt 0) statement2 / if 0 lt i lt 10
then execute statement2 / if (a1
a2) statement3 / if a1 a2 then execute
statement3 / Control Flow - The control-flow
statements specify the order in which
computations are performed. - Semicolon is a
statement terminator. - Braces and are used
to group declarations and statements together
into a compound statement, or block.
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If-Else Statement if (expression) statement1
else -- The else part is optional. statement2
Example, if (a ! 0) r b else r
c A more concise way for this statement is r
(a ! 0)? b c
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Multiway Conditional Statement if
(expression1) statement1 else if
(expression2) statement2 else if
(expression3) statement3 else statementn
Example, if (abc gt 0) return 5 else if (abc
0) return 0 else return -5
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Switch Statement Example switch (expression)
switch (i) case const_expr1 case 1
printf() statement1 break break
case 2 printf() case const_expr2 break
statement2 case 3 printf() break
break case 4 printf() default
break statementn case 5
printf() break
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For-Loop Statement for (expr1 expr2
expr3) statement where, expr1 and expr2 are
assignments or function calls and expr3 is a
relational expression. Example sum 0 for
(i 1 i lt 10 i) sum i i for (i
1 i lt 20 i) if (i 2) printf(d , i)
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While Statement while (expression) statement
Example int_cnt 5 while (int_cnt) / do
nothing while the variable int_cnt ? 0
/ Do-While Statement Example do int digit
9 statement do while (expression) printf(d
, digit--) while (digit gt 1)
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Input and Output Examples - Not part of the C
language itself. - Four I/O functions will be
discussed. 1. int getchar ( ). char xch --
returns a character when called xch getchar
() 2. int putchar (int). putchar(a) --
outputs a character on a standard output
device 3. int puts (const char s). puts
(Welcome to USA! \n) -- outputs the string
pointed by s on a standard output
device 4. int printf (formatting string, arg1,
arg2, ). -- converts, formats, and prints its
arguments on the standard output device.
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Formatting String for Printf - The arguments of
printf can be written as constants, single
variable or array names, or more complex
expressions. - The formatting string is composed
of individual groups of characters, with
one character group associated with each output
data item. - The character group starts with .
- The simplest form of a character group
consists of the percent sign followed by a
conversion character indicating the type of the
corresponding data item. - Multiple character
groups can be contiguous, or they can be
separated by other characters, including
whitespace characters. These other characters
are simply sent to the output device for
display. - Examples printf (this is a
challenging course ! \n) printf(d d d, x1,
x2, x3) / outputs x1, x2, and x3 using minimal
number of digits with one space
separating each value / printf(Todays
temperature is 4.1d\n, temp)
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Rules for Conversion String - Between the and
the conversion character there may be, in
order 1. A minus sign, -- specify left
adjustment. 2. A number that specifies the
minimum field width. 3. A period that separates
the field width from precision. 4. A number, the
precision, that specifies the maximum number of
characters to be printed from a string, or the
number of digits after the decimal point,
or the minimum of digits for an integer. 5. An
h if the integer is to be printed as a short, or
l (letter ell) if as a long.
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Functions and Program Structure - Every C
program consists of one or more
functions. - Definition of a function cannot be
embedded within another function. - A function
will process information passed to it from the
calling portion of the program, and return a
single value. - Syntax of a function
definition return_type function_name
(declarations of arguments) declarations and
statements Example char lower2upper (char
cx) if cx gt a cx lt z) return (cx -
(a - A)) else return cx
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Example 4.1 Write a function to test if an
integer is a prime number. Solution A number is
a prime if it is indivisible by any integer
between 2 and half of itself. / this function
returns a 1 if a is prime. Otherwise, it returns
a 0. / char test_prime (int a) int i if (a
1) return 0 for (i 2 i lt a/2 i) if
((a i) 0) return 0 return 1 - A
function must be defined before it can be
called. - Function prototype declaration allows
us to call a function before it is
defined. - Syntax of a function prototype
declaration return_type function_name
(declarations of arguments)
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Example 4.2 Write a program to find out the
number of prime numbers between 100 and
1000. Solution include ltstdio.hgt char
test_prime (int a) / prototype declaration for
the function test_prime / main ( ) int i,
prime_count 0 for (i 100 i lt 1000 i)
if (test_prime(i)) prime_count
printf(\n The total prime numbers
between 100 and 1000 is d\n, prime_count) ch
ar test_prime (int a) int i if (a 1)
return 0 for (i 2 i lt a/2 i) if ((a
i) 0) return 0 return 1
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Pointers and Addresses - A pointer is a variable
that holds the address of a variable. - Pointers
provide a way to return multiple data items from
a function via function arguments. - Pointers
also permit references to other functions to be
specified as arguments to a given
function. - Syntax for pointer declaration type
_name pointer_name Examples int ax char
cp - Use the dereferencing operator to
access the value pointed by a pointer. int a,
b a b / assigns the value pointed by
b to a /
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- Use the unary operator to assign the address
of a variable to a pointer. For example, int
x, y int ip ip x y ip / y gets
the value of x /
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Example 4.3 Write a bubble sort function to sort
an array of integers. Solution void swap (int
, int ) / function prototype declaration
/ void bubble (int a, int n) / n is the array
count / int i, j for (i 0 i lt n - 1
i) for (j n - 1 j gt i j--) if (aj -
1 gt aj) swap (aj - 1, aj) void
swap(int px, int py) int temp temp
px px py py temp
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Arrays - An array consists of a sequence of data
items that have common characteristics. - Each
array is referred to by specifying the array name
followed by one or more subscripts, with each
subscript enclosed in brackets. Each subscript is
a nonnegative integer. - The number of subscripts
determines the dimensionality of the array. For
example, xi is an element of an
one-dimensional array yij refers to an
element of a two-dimensional array - Syntax for
one-dimensional array declaration data-type
array_name expression - Syntax for
two-dimensional array declaration data-type
array_name expr1 expr2
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Pointers and Arrays - Any operations that can be
achieved by array subscripting can also be done
with pointers. - The pointer version will in
general be faster but, somewhat harder to
understand. - For example, int ax20 /
array of 20 integers / int ip / ip is an
integer pointer / ip ax0 / ip contains
the address of ax0 / x ip / copy the
contents of ax0 into x. - If ip points to
ax0, then ip 1 points to ax1, and ip i
points to axi, etc.
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Passing Arrays to a Function - An array name can
be used as an argument to a function. - To pass
an array to a function, the array name must
appear by itself, without brackets
or subscripts, as an actual argument within the
function call. - When declaring a one-dimensional
array as a formal argument, the array name is
written with a pair of empty square
brackets. - When declaring a two-dimensional
array as a formal argument, the array name is
written with two pairs of empty square
brackets. - Example, int average (int n, int
arr ) main ( ) int n, avg int
arr50 avg average (n, arr) /
function call with array name as an argument
/ int average (int k, int brr ) /
function definition /
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External Variables - A variable declared inside
a function is called an internal variable. - A
variable defined outside of a function is called
a external variable. - An external variable is
available to many functions. - External variables
provide an alternative to function arguments and
return values for communicating data between
functions. - Any function may access an external
variable by referring to it by name if the the
name has been declared somewhere. Scope
Rules - The functions and external variables
that make up a C program can be compiled
separately. - The source text of the program may
be kept in several files. - The scope of a name
is the part of the program within which the name
can be used. - For a variable declared at the
beginning of a function, the scope is the
function in which the name is declared. - Local
(internal) variables of the same name in
different functions are unrelated. - The scope of
an external variable or a function lasts from the
point at which it is declared to the end of the
file being compiled.
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In the following program segment The use of
external variables are illustrated in the
following 2-file C program in file 1 void f1
() extern int xy extern long arr
main ( ) int a, b, c void
f2() void foo (int abc) long soo (void)
in file 2 int xy Variables a, b,
and c are accessible to long arr 100 function
f2 but not f1.
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Using the ImageCraft C Compiler - An Integrated
Development Software (IDS) may consist of a text
editor, a compiler, a linker, a librarian, an
assembler, a simulator, and debugger, etc. - An
IDS uses project as the unit to control the
software development. - A user creates C
functions in one or multiple files using the
editor provided by the integrated software. - The
compiler is then invoked to compile each
individual file. In most cases, you will need
to eliminate syntax errors in this
step. - Create a new project and add the files
just created into this project. - Build the
project. The IDS will combine all object modules
into one executable module and may translate it
into appropriate format suitable for downloading
into a demo board for execution. - Download the
module into a demo board for execution. - In the
following, we will use a project that consists of
a single file to illustrate the process of using
the ImageCraft C compiler for program development
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Step 1. Invoke the ICC11 by clicking the icon of
ICC1 program. A window appears as follows
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Step 2. Click the file menu and select new to
create a new file for entering a new
program. The screen look like this
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Step 3. Type in the new program and save it in an
appropriate directory. An example is shown in
Figure 4.3.
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Step 4. Create a new project by clicking the
project menu and select new. The screen is
shown in Figure 4.4. After selecting new, the
screen changes to Figure 4.5. After this, we need
to enter the project name and the result is
shown in Figure 4.6.
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Step 5. Add the program to the newly created
project. Press the Add button on Figure 4.6. A
list of files will be displayed and you can
select those files that you want to include
in this project. Click on the file add.c and the
result is shown in Figure 4.7.
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Step 6. Setting appropriate options for the
compiler, editor, and terminal program. The
options available can be seen by pressing the
Options menu shown in Figure 4.8.
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Step 7. Set compiler preprocessor options. There
are three sets of options that need to be set in
the compiler preprocessor, compiler, and linker.
Select Compiler in Figure 4.8 and then click on
Preprocessor and the screen shown in Figure 4.9a
will be brought up. Enter the appropriate
include path. Do not click on OK.
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Step 8. Set compiler options. Click on the item
compiler. The default options shown in Figure
4.9b are OK.
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Step 9. Set linker options. Click the Linker
button on Figure 4.9a to bring up the linker
option screen. The appropriate option values
for EVB demo board are shown in Figure 4.9c. The
appropriate option values for CMD11A8 are shown
in Figure 4.9d.
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Step 10. Set terminal options. Go back to Option
menu and select Terminal. This will bring up the
terminal option screen as shown in Figure 4.10.
The com port can be com1 or com2. Baud rate
should be set to 9600 for both EVB and CMD11A8.
Flow control should be set to none. Font also
need to set properly. A popular font is Courier
or Courier New (shown in Figure 4.11). Click on
OK and the screen will change back to Figure 4.8.
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Step 10. Build the project. Click the Build
button and ICC11 will start to process your
file. The Build button will be dimmed before it
is done. When it is done, the Build button
will change back to bold. Minimize both the
project and source code windows and maximize
the status window and the result is shown in
Figure 4.12.
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Step 11. Download the program onto the demo board
for execution. Click the Target menu and select
Terminal and this will bring up the terminal
window as shown in Figure 4.13. Type load t
followed by the enter key, and click on the
Browse button. This would bring up a popup
window (shown in Figure 4.14) for you to select a
file to download. Select add.s19 and click OK
button. Click the ASCII Download button to start
downloading. The downloading process looks like
that in Figure 4.15. A successful download should
look like Figure 4.16.
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Select a File to Download
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Download Process
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A Successful Download
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Step 12. Program Execution and Debugging. ICC11
terminal program allows you to use all the
Buffalo commands to debug the program when using
an EVB and CMD11A8 demo board. Type G 2000 to
run this program on the CMD11A8 demo board and
the result would look like Figure 4.17. (Type G
C000 on the EVB board).