L12 c-language-programming-of-atmega328 p

C Programming of Atmega328P
(Lecture-12)
R S Ananda Murthy
Associate Professor and Head
Department of Electrical & Electronics Engineering,
Sri Jayachamarajendra College of Engineering,
Mysore 570 006
R S Ananda Murthy C Programming of Atmega328P

Merits and Demerits of C Programming AVR MCU
Merits
Lesser time consuming and easier than ALP.
C programs can be easily ported to some other
microcontroller with minor modifications.
C programs are less error prone when compared to ALP.
Readiliy available C function libraries can be used to reduce
development time.
Demerits
C compilers do not produce optimized hex files.
Improper use of data types by the programmer can lead to
larger hex file size.
The programmer does not have direct access to general
purpose registers in C programs.

Some Prominent AVR C Compilers
AVR-GCC in Atmel Studio on Windows platforms.
AVR-GCC in GNU Linux environment. URL:
http://www.gnu.org/software/gcc/
microC PRO for AVR. URL:
http://www.mikroe.com/mikroc/avr/
CrossWorks for AVR. URL:
http://www.rowley.co.uk/avr/
JumpStart C Tools for AVR. https:
//www.imagecraft.com/devtools_AVR.html
AVR-GCC is the most popular compiler in industry.

C Data Types in AVR-GCC
Data Type Size in Bits Data Range
unsigned char 8-bit 0 to 255
char 8-bit −128 to +127
unsigned int 16-bit 0 to 65,535
int 16-bit −32768 to +32767
unsigned long 32-bit 0 to 4294967295
long 32-bit
−2147483648 to
+2147483648
ﬂoat 32-bit ±1.175e −38 to ±3.402e38
double 32-bit ±1.175e −38 to ±3.402e38
Using improper data type results in larger hex ﬁle.

Data Type for AVR C Programming
Based on the knowledge of range of data, always use the
data type having the smallest range to accommodate the
data.
As far as possible, unsigned char data type should be used
since most of the data handled by the AVR MCU is in the
range 0 to 255 or $00 to $FF.
Using int data type instead of char type can result in larger
hex ﬁles.

AVR C Program Sample-1
All AVR C programs will be inﬁnite loops as shown above.
The above program outputs $00 to $FF to continuously.

AVR C Program Sample-2
Inﬁnite loop is caused by while(1) statement.
The above program outputs 0, 1, 2, 3, 4, 5, A, B, C, and D
to PORTB.

Methods of Realizing Time Delay in C
By using simple for loop.
This method does not give accurate time delays because
the actual delay depends upon the length of the hex file
generated by the compiler which varies from one compiler
to another and also on the clock frequency of MCU. For
these reasons, we have to measure the actual delay using
an oscilloscope.
By using predefined C functions.
_delay_ms() function can be used to cause several ms
delay and _delay_us() can be used to cause several µs
delay. Both of these functions are defined in avr-libc in
delay.h header file. See avr-libc documentation available
at http://avr-libc.nongnu.org/user-manual/
group__util__delay.html
By using timers in the MCU.

Delay by FOR Loop
This program toggles bits of PORTB continuously with a delay.

Delay by using _delay_ms() Function
This program blinks LED at PB2 with a delay of 100 ms.

Delay by using _delay_us() Function
This program blinks LED at PB2 with a delay of 100 µs.

Input and Output Operations in C
This program reads a byte from Port C. If it is less than 100, it
will send it to Port B; otherwise it will send it to Port D.

Logic Operations in C
In the program given above ﬁnd the output at each port after
each logical operation.

Bit-wise Shift Operations in C

Bit-wise Operations in C

Multiple Branching using Switch

License
This work is licensed under a
Creative Commons Attribution 4.0 International License.

L12 c-language-programming-of-atmega328 p

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