UART protocol fundamentals in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

UART Transmission Bit Timing Calculation

Given a UART baud rate of 9600 and a system clock of 16 MHz, what is the value of the UART bit time in microseconds calculated by the code below?

Embedded C

unsigned int baud_rate = 9600;
unsigned long clock_freq = 16000000;
float bit_time_us = (1.0 / baud_rate) * 1000000;

// Print bit time
printf("%.2f\n", bit_time_us);

A 16.00

B 9600.00

C 104.17

D 1.60

💡 Hint

Remember that bit time is the inverse of baud rate, converted to microseconds.

Bit time is the duration of one bit. It is calculated as 1 divided by baud rate. For 9600 baud, bit time = 1/9600 = 0.00010417 seconds = 104.17 microseconds.

❓ Predict Output

intermediate

UART Frame Size Calculation

What is the total number of bits transmitted in one UART frame with 1 start bit, 8 data bits, no parity, and 1 stop bit?

A 10

B 9

C 11

D 8

💡 Hint

Add start bits, data bits, parity bits (if any), and stop bits.

UART frame bits = start bit (1) + data bits (8) + parity bits (0) + stop bits (1) = 10 bits total.

🔧 Debug

advanced

Identify the UART Configuration Error

The following UART initialization code is intended to set 8 data bits, even parity, and 1 stop bit. Which option correctly identifies the error causing wrong parity configuration?

Embedded C

UART_Config config;
config.data_bits = 8;
config.parity = 0; // 0 means no parity
config.stop_bits = 1;
UART_Init(&config);

A Data bits should be set to 7 for even parity to work.

B Parity is set to 0 which disables parity; should be set to 2 for even parity.

C Stop bits must be 2 for parity to be enabled.

D UART_Init function is missing baud rate parameter.

💡 Hint

Check the parity value and what it represents.

Parity value 0 disables parity. For even parity, the code should set parity to 2 (assuming 2 means even parity in this API).

📝 Syntax

advanced

UART Interrupt Handler Syntax

Which option shows the correct syntax for a UART receive interrupt handler function in embedded C?

A void UART_RX_IRQHandler(void) { /* handle RX interrupt */ }

B UART_RX_IRQHandler(void) { /* handle RX interrupt */ }

C void UART_RX_IRQHandler(int irq) { /* handle RX interrupt */ }

D int UART_RX_IRQHandler() { /* handle RX interrupt */ }

💡 Hint

Interrupt handlers usually return void and take no parameters.

The correct syntax is a void function with no parameters for interrupt handlers in embedded C.

🚀 Application

expert

UART Data Buffer Overflow Scenario

In a UART communication system, if the receive buffer is not read fast enough and new data keeps arriving, what will happen?

A The UART will store all data indefinitely without loss.

B The UART hardware will automatically pause transmission until buffer is free.

C The system will raise a hardware exception and reset the UART module.

D New incoming data will overwrite old unread data causing data loss.

💡 Hint

Think about what happens when a fixed-size buffer is full and new data arrives.

If the receive buffer is full and not read, new data overwrites old data causing loss. UART hardware usually does not pause transmission automatically.