I2C bus architecture (SDA, SCL) in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the I2C data line (SDA) pin.

Embedded C

const int SDA_PIN = [1];

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

A5

B21

C13

D19

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing the SCL pin number instead of SDA.

The SDA line is commonly assigned to pin 21 in many microcontroller boards.

2fill in blank

medium

Complete the code to define the I2C clock line (SCL) pin.

Embedded C

const int SCL_PIN = [1];

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

A21

B18

C5

D22

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing SDA and SCL pin numbers.

The SCL line is commonly assigned to pin 22 in many microcontroller boards.

3fill in blank

hard

Fix the error in the I2C initialization function to set SDA and SCL pins correctly.

Embedded C

void i2c_init() {
    i2c_config_t conf;
    conf.sda_io_num = [1];
    conf.scl_io_num = 22;
    // other config code
}

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

A21

B5

C18

D19

Attempts:

3 left

💡 Hint

Common Mistakes

Setting SDA pin to the SCL pin number by mistake.

The SDA pin must be set to 21 to match the hardware wiring.

4fill in blank

hard

Fill both blanks to complete the I2C configuration struct with correct SDA and SCL pins.

Embedded C

i2c_config_t conf = {
    .sda_io_num = [1],
    .scl_io_num = [2],
    .mode = I2C_MODE_MASTER
};

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

A21

B22

C18

D19

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping SDA and SCL pin numbers.

SDA is pin 21 and SCL is pin 22 for the I2C master configuration.

5fill in blank

hard

Fill all three blanks to complete the I2C master initialization with correct pins and clock speed.

Embedded C

i2c_config_t conf = {
    .sda_io_num = [1],
    .scl_io_num = [2],
    .master.clk_speed = [3]
};

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

A21

B22

C100000

D400000

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong pins or incorrect clock speed values.

The SDA pin is 21, SCL pin is 22, and the clock speed is set to 100000 Hz (100 kHz standard speed).

Practice

1. Which two lines are used in the I2C bus architecture for communication?

easy

A. CLK for data and DAT for clock

B. TX for data and RX for clock

C. SDA for data and SCL for clock

D. MOSI for data and MISO for clock

Solution

1. Step 1: Recall I2C bus lines

   I2C uses two specific lines: SDA and SCL.

2. Step 2: Identify roles of lines

   SDA carries data, and SCL carries the clock signal.

3. Final Answer:

   SDA for data and SCL for clock -> Option C

4. Quick Check:

   I2C lines = SDA + SCL [OK]

Hint: Remember: SDA = data, SCL = clock [OK]

Common Mistakes:

• Confusing I2C lines with SPI lines
• Mixing data and clock line names
• Assuming more than two lines are used

2. Which of the following correctly describes the state of the SDA and SCL lines when no device is pulling them low on an I2C bus?

easy

A. SDA is high, SCL is low

B. Both lines are low

C. SDA is low, SCL is high

D. Both lines are high

Solution

1. Step 1: Understand line behavior on I2C bus

   Lines are open-drain and pulled high by resistors when released.

2. Step 2: Determine line state when idle

   When no device pulls lines low, both SDA and SCL remain high.

3. Final Answer:

   Both lines are high -> Option D

4. Quick Check:

   Idle I2C lines = high [OK]

Hint: Lines float high unless pulled low [OK]

Common Mistakes:

• Assuming lines default to low
• Confusing line states during communication
• Ignoring pull-up resistor effect

3. Consider this snippet controlling I2C lines in embedded C:

if (SDA == 1 && SCL == 1) {
    // Start condition detected
} else if (SDA == 0 && SCL == 1) {
    // Stop condition detected
}

What is the output behavior of this code snippet?

medium

A. Detects start when SDA goes low while SCL is high

B. Detects stop when SDA goes high while SCL is low

C. Detects start when SDA and SCL are both low

D. Detects stop when SDA and SCL are both high

Solution

1. Step 1: Recall I2C start and stop conditions

   Start condition: SDA falls low while SCL is high. Stop condition: SDA rises high while SCL is high.

2. Step 2: Analyze code conditions

   The code checks if SDA and SCL are both high for start, which is incorrect; start is when SDA falls low while SCL is high.

3. Final Answer:

   Detects start when SDA goes low while SCL is high -> Option A

4. Quick Check:

   Start = SDA low + SCL high [OK]

Hint: Start = SDA falls low while SCL high [OK]

Common Mistakes:

• Mixing start and stop conditions
• Checking both lines high for start
• Ignoring SDA line change direction

4. This embedded C code snippet is intended to detect an I2C stop condition:

if (SDA == 1 && SCL == 0) {
    // Stop condition detected
}

What is the error in this code?

medium

A. Stop condition requires SCL to be high, not low

B. SDA should be low, not high for stop condition

C. Both SDA and SCL should be low for stop condition

D. No error; code correctly detects stop condition

Solution

1. Step 1: Recall stop condition timing

   Stop condition occurs when SDA rises from low to high while SCL is high.

2. Step 2: Check code condition

   The code checks SDA high and SCL low, which is incorrect; SCL must be high for stop.

3. Final Answer:

   Stop condition requires SCL to be high, not low -> Option A

4. Quick Check:

   Stop = SDA high + SCL high [OK]

Hint: Stop needs SCL high, not low [OK]

Common Mistakes:

• Confusing clock line state for stop
• Assuming SDA low means stop
• Ignoring line state transitions

5. You want to implement a function in embedded C that waits for the I2C start condition before proceeding. Which logic correctly detects the start condition on SDA and SCL lines?

hard

A. Wait until SDA changes from low to high while SCL is low

B. Wait until SDA changes from high to low while SCL is high

C. Wait until both SDA and SCL are low simultaneously

D. Wait until SCL changes from low to high while SDA is low

Solution

1. Step 1: Understand start condition in I2C

   Start condition is when SDA line falls from high to low while SCL line is high.

2. Step 2: Match logic to condition

   Wait until SDA changes from high to low while SCL is high correctly waits for SDA falling edge with SCL high, matching start condition.

3. Final Answer:

   Wait until SDA changes from high to low while SCL is high -> Option B

4. Quick Check:

   Start = SDA high-to-low + SCL high [OK]

Hint: Start = SDA falls low while SCL high [OK]

Common Mistakes:

• Waiting for SDA rising edge instead of falling
• Checking SCL low instead of high
• Confusing start with stop condition