UART protocol fundamentals in Embedded C - Mini Project: Build & Apply

UART Protocol Fundamentals

📖 Scenario: You are working on a small embedded system that communicates with a sensor using UART (Universal Asynchronous Receiver/Transmitter). You need to set up the UART data buffer and process the data bytes received.

🎯 Goal: Build a simple UART data handler in C that stores received bytes in a buffer, counts how many bytes are received, and prints the buffer content.

📋 What You'll Learn

Create a buffer array to hold UART data bytes

Create a variable to count the number of bytes received

Use a loop to simulate receiving bytes and store them in the buffer

Print the received bytes as hexadecimal values

💡 Why This Matters

🌍 Real World

Embedded systems often use UART to communicate with sensors, modules, or other microcontrollers. Handling UART data buffers is essential for reliable data exchange.

💼 Career

Understanding UART protocol basics is important for embedded software developers working on hardware communication, device drivers, or IoT devices.

1

Create UART data buffer

Create an array called uart_buffer of type unsigned char with size 5 to hold UART data bytes.

Embedded C

# Create an array called uart_buffer of unsigned char with size 5
// Your code here

Hint

Think of uart_buffer as a small box that can hold 5 bytes of data.

2

Create byte count variable

Create an integer variable called byte_count and initialize it to 0 to count how many bytes are received.

Embedded C

unsigned char uart_buffer[5];
// Create an integer variable byte_count and set it to 0
// Your code here

Hint

This variable will keep track of how many bytes you have stored in the buffer.

3

Store received bytes in buffer

Use a for loop with variable i from 0 to 4 to simulate receiving bytes. Store the values 0x10 + i into uart_buffer[i]. After storing each byte, increase byte_count by 1.

Embedded C

unsigned char uart_buffer[5];
int byte_count = 0;
// Use a for loop with i from 0 to 4 to store bytes 0x10+i into uart_buffer[i]
// Increase byte_count by 1 each time
// Your code here

Hint

Imagine you receive bytes 0x10, 0x11, 0x12, 0x13, 0x14 one by one and store them in the buffer.

4

Print received UART bytes

Use a for loop with variable i from 0 to byte_count - 1 to print each byte in uart_buffer as hexadecimal using printf with format "0x%02X ". After the loop, print a newline.

Embedded C

unsigned char uart_buffer[5];
int byte_count = 0;

for (int i = 0; i < 5; i++) {
    uart_buffer[i] = 0x10 + i;
    byte_count++;
}

// Print each byte in uart_buffer as hex with printf
// Your code here

Hint

This will show the bytes you stored, like reading the data from the UART line.

Practice

1. What does UART stand for in embedded systems communication?

easy

A. Universal Analog Radio Transmitter

B. Universal Automatic Register Transfer

C. Unified Asynchronous Remote Terminal

D. Universal Asynchronous Receiver/Transmitter

Solution

1. Step 1: Understand UART acronym

   UART is a communication protocol used in embedded systems for serial communication.

2. Step 2: Match full form

   UART stands for Universal Asynchronous Receiver/Transmitter, describing its function.

3. Final Answer:

   Universal Asynchronous Receiver/Transmitter -> Option D

4. Quick Check:

   UART = Universal Asynchronous Receiver/Transmitter [OK]

Hint: Remember UART is about asynchronous serial communication [OK]

Common Mistakes:

• Confusing UART with synchronous protocols
• Mixing up the acronym words
• Thinking UART is analog communication

2. Which of the following is the correct way to initialize UART in embedded C?

easy

A. uart_init(9600);

B. UART_Init(baudrate=9600);

C. uartStart(9600);

D. init_uart(9600);

Solution

1. Step 1: Identify common UART init function

   In embedded C, uart_init with baud rate parameter is a common initialization call.

2. Step 2: Check syntax correctness

   uart_init(9600); uses correct function name and parameter style without extra keywords.

3. Final Answer:

   uart_init(9600); -> Option A

4. Quick Check:

   Correct UART init syntax = uart_init(9600); [OK]

Hint: Look for simple function call with baud rate only [OK]

Common Mistakes:

• Using incorrect function names
• Adding parameter names inside call
• Using camelCase instead of snake_case

3. What will be the output of this UART send code snippet?

uart_init(9600);
uart_send_char('A');
uart_send_char('B');

medium

A. BA

B. A B

C. AB

D. Error: uart_send_char undefined

Solution

1. Step 1: Initialize UART at 9600 baud

   The uart_init(9600) sets baud rate for communication.

2. Step 2: Send characters in order

   uart_send_char('A') sends 'A', then uart_send_char('B') sends 'B' sequentially.

3. Final Answer:

   AB -> Option C

4. Quick Check:

   Characters sent in order = AB [OK]

Hint: Characters send in call order, no spaces added [OK]

Common Mistakes:

• Assuming characters reverse order
• Expecting spaces between characters
• Thinking uart_send_char is undefined

4. Identify the error in this UART initialization code:

void setup() {
  uart_init(115200);
  uart_init(9600);
}

medium

A. uart_init requires no parameters

B. Multiple uart_init calls cause baud rate conflict

C. Function name should be UART_Init

D. No error, code is correct

Solution

1. Step 1: Review uart_init calls

   Two uart_init calls with different baud rates cause conflict in configuration.

2. Step 2: Understand UART config rules

   UART baud rate must be set once before communication; multiple calls overwrite settings.

3. Final Answer:

   Multiple uart_init calls cause baud rate conflict -> Option B

4. Quick Check:

   Multiple init calls cause conflict = A [OK]

Hint: Only one uart_init call needed to set baud rate [OK]

Common Mistakes:

• Thinking multiple init calls are allowed
• Assuming uart_init has no parameters
• Ignoring case sensitivity in function names

5. You want to send the string "HELLO" over UART. Which code snippet correctly sends each character one by one?

hard

A. for(int i=0; i<5; i++) uart_send_char("HELLO"[i]);

B. for(int i=0; i<5; i++) uart_send_char('H' + i);

C. for(int i=0; i<5; i++) uart_send_char('HELLO'[i]);

D. for(int i=0; i<5; i++) uart_send_char("HELLO" + i);

Solution

1. Step 1: Understand string indexing in C

   In C, single quotes ' ' denote characters, double quotes \" \" denote strings (char arrays).

2. Step 2: Check each option for correct character access

   for(int i=0; i<5; i++) uart_send_char(\"HELLO\"[i]); correctly indexes the string literal to access each character 'H','E','L','L','O'.

3. Final Answer:

   for(int i=0; i<5; i++) uart_send_char("HELLO"[i]); -> Option A

4. Quick Check:

   Correct string indexing uses double quotes \"HELLO\"[i] [OK]

Hint: Use double quotes for string literal indexing in C [OK]

Common Mistakes:

• Using single quotes for multi-character string literals
• Adding integers to characters ('H' + i sends HIJKL)
• Using pointer arithmetic without dereferencing