1. Embedded Programming in C
Presented by:
Jered Aasheim
Tom Cornelius
January 11, 2000

2. Why Use C?
C allows the programming low-level access to the machine architecture.
Compiled C programs are memory efficient and can execute very fast.
Higher level language constructs allow designs to be more complicated, reduce the number of bugs, and help get more done per unit of time.

3. Data Types Type Size (bits) Dynamic Range unsigned char 8 0…255
-128…127
unsigned int 16
0…65,535
signed int
-32,678…32,677
unsigned long 32
0…4,294,967,295
signed long
-2,147,483,647…
2,147,483,647

4. Number Representation
In C, numbers can be expressed in decimal, hexadecimal, or octal:
Decimal 2 63 83
Octal 00 02
077
0123
Hexadecimal
0x0
0x2
0x3F
0x53

5. Bit Manipulation
<<, >> - shifts value k bits to the left or right
ex. 0x08 >> // 0x01
& - bitwise ANDs two operands together
ex. 0x08 & 0xF0 // 0x00
| - bitwise ORs two operands together
ex. 0x08 | 0xF // 0xF8
^ - bitwise XORs two operands together
ex. 0xAA ^ 0xFF // 0x55

6. Reading/Writing Individual Bits
The bitwise AND and OR operators can be used to read/write individual bits in a variable:
Ex.
unsigned char reg = 0xB5;
if(reg & 0x08) // Is the 4th bit a “1”? …
else // 4th bit is not a “1”
reg = reg | 0x02; // Set the 2nd bit to a “1”
reg = reg & 0xFE; // Set the 1st bit to a “0”

7. Scope There are 3 ways to declare a variable – global, local, static:
ex. unsigned char inputStatus; // global
ex. void f(void) { int sum; … } // local
ex. void g(void) { static char ttlLine; … } // static
The static keyword means that the variable will retain its value across function calls; there are situations where this is very useful for retaining state in a subroutine/function.

8. Infinite Program Loop
Embedded systems are usually meant to always execute the same program for the duration of the time the device is on. This can be done using a “forever loop”:
void main(void) { …
for(;;)
// main program loop }