UART protocol fundamentals in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize UART baud rate register.

Embedded C

UART_BAUD_REG = [1];

Drag options to blanks, or click blank then click option'

A103

B9600

C115200

D0xFF

Attempts:

3 left

💡 Hint

Common Mistakes

Using baud rate number directly instead of register value.

The baud rate register value for 9600 baud at 16 MHz clock is 103.

2fill in blank

medium

Complete the code to enable UART transmitter.

Embedded C

UART_CTRL_REG |= [1];

Drag options to blanks, or click blank then click option'

A0x08

B0x04

C0x10

D0x01

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing transmitter enable with receiver enable bits.

Bit 2 (0x04) enables the UART transmitter in control register.

3fill in blank

hard

Fix the error in the UART receive function to correctly check data ready flag.

Embedded C

if (UART_STATUS_REG & [1]) {
    received_data = UART_DATA_REG;
}

Drag options to blanks, or click blank then click option'

A0x20

B0x80

C0x40

D0x10

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong status flag bit causing missed data reception.

Bit 6 (0x40) is the RX complete flag indicating data is ready to read.

4fill in blank

hard

Fill both blanks to create a UART transmit function that waits until ready and sends data.

Embedded C

while (!(UART_STATUS_REG & [1])) {}
UART_DATA_REG = [2];

Drag options to blanks, or click blank then click option'

A0x20

Bdata

C0x80

D0x40

Attempts:

3 left

💡 Hint

Common Mistakes

Waiting on wrong flag or writing wrong variable to data register.

Wait for transmit buffer empty flag (bit 5, 0x20) before writing data to UART_DATA_REG.

5fill in blank

hard

Fill all three blanks to create a UART initialization function setting baud rate, enabling transmitter and receiver.

Embedded C

void UART_Init() {
    UART_BAUD_REG = [1];
    UART_CTRL_REG = [2] | [3];
}

Drag options to blanks, or click blank then click option'

A103

B0x04

C0x08

D9600

Attempts:

3 left

💡 Hint

Common Mistakes

Using baud rate number directly, forgetting to enable both transmitter and receiver.

Set baud rate register to 103 for 9600 baud, enable transmitter (0x04) and receiver (0x08) bits in control register.

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