Multi-channel ADC scanning in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start ADC conversion.

Embedded C

ADC_Start([1]);

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AADC_CHANNEL_2

BADC_CHANNEL_1

CADC_CHANNEL_0

DADC_CHANNEL_3

Attempts:

3 left

💡 Hint

Common Mistakes

Using a channel number that is not defined or out of range.

The function ADC_Start requires the channel number to start conversion. Here, ADC_CHANNEL_0 is the first channel.

2fill in blank

medium

Complete the code to read the ADC value from the specified channel.

Embedded C

uint16_t value = ADC_Read([1]);

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AADC_CHANNEL_1

BADC_CHANNEL_2

CADC_CHANNEL_3

DADC_CHANNEL_0

Attempts:

3 left

💡 Hint

Common Mistakes

Reading from a channel that was not started or configured.

The ADC_Read function reads the value from the given channel. Here, ADC_CHANNEL_0 is used to read from the first channel.

3fill in blank

hard

Fix the error in the code to correctly configure ADC for multi-channel scanning.

Embedded C

ADC_ConfigTypeDef adcConfig;
adcConfig.scanConvMode = [1];
adcConfig.continuousConvMode = ENABLE;

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ADISABLE

BENABLE

CSTART

DSTOP

Attempts:

3 left

💡 Hint

Common Mistakes

Setting scan mode to DISABLE disables multi-channel scanning.

To enable multi-channel scanning, scanConvMode must be set to ENABLE.

4fill in blank

hard

Fill both blanks to set the number of channels and the first channel in the ADC sequence.

Embedded C

adcConfig.NbrOfConversion = [1];
adcConfig.Channel = [2];

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A3

BADC_CHANNEL_0

CADC_CHANNEL_1

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the wrong number of conversions or wrong starting channel.

The number of conversions is set to 3, and the first channel in the sequence is ADC_CHANNEL_0.

5fill in blank

hard

Fill all three blanks to complete the loop that reads ADC values from multiple channels.

Embedded C

for (int i = 0; i < [1]; i++) {
    adcValues[i] = ADC_Read([2] + i);
}
ProcessValues(adcValues, [3]);

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A4

BADC_CHANNEL_0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong loop count or wrong channel start index.

The loop runs 3 times to read 3 channels starting from ADC_CHANNEL_0. The processing function is called with 3 values.

Practice

1.

What is the main purpose of multi-channel ADC scanning in embedded C?

easy

A. To read multiple analog inputs one after another automatically

B. To write digital output signals to multiple pins

C. To increase the clock speed of the microcontroller

D. To store data in external memory

Solution

1. Step 1: Understand ADC scanning concept

   Multi-channel ADC scanning reads several analog inputs sequentially without manual switching.

2. Step 2: Identify the purpose

   This allows efficient sensor data collection from multiple sources automatically.

3. Final Answer:

   To read multiple analog inputs one after another automatically -> Option A

4. Quick Check:

   Multi-channel ADC scanning = reading multiple analog inputs [OK]

Hint: Remember ADC scanning reads many inputs in sequence [OK]

Common Mistakes:

• Confusing ADC scanning with digital output control
• Thinking it speeds up the microcontroller clock
• Assuming it stores data externally

2.

Which of the following code snippets correctly initializes a multi-channel ADC scan for 3 channels in embedded C?

void ADC_Init() {
    ADCON0 = 0x01; // Enable ADC
    ADCON1 = 0x00; // Configure ports as analog
    ADCON2 = 0xA9; // Right justify, 12 TAD, Fosc/8
    // Missing code here
}

easy

A. ADCHS = 0x00; // Select channel 0 only

B. ADCHS = 0x03; // Select channels 0 and 1 only

C. ADCHS = 0xFF; // Select all channels

D. ADCHS = 0x07; // Select channels 0 to 2 for scanning

Solution

1. Step 1: Understand ADCHS register role

   ADCHS selects which ADC channels to scan; bits 0-2 correspond to channels 0-2.

2. Step 2: Choose correct bitmask for 3 channels

   0x07 in binary is 00000111, enabling channels 0,1,2 for scanning.

3. Final Answer:

   ADCHS = 0x07; // Select channels 0 to 2 for scanning -> Option D

4. Quick Check:

   0x07 = channels 0,1,2 selected [OK]

Hint: Use bitmask 0x07 to select first 3 ADC channels [OK]

Common Mistakes:

• Selecting only one channel instead of multiple
• Using 0xFF which may select invalid channels
• Confusing ADCHS with ADCON registers

3.

Consider the following embedded C code snippet for multi-channel ADC scanning:

int adc_values[3];
for(int ch = 0; ch < 3; ch++) {
    ADCON0 = (ch << 2) | 0x01; // Select channel and turn on ADC
    __delay_ms(2); // Acquisition time
    ADCON0 |= 0x02; // Start conversion
    while(ADCON0 & 0x02); // Wait for conversion
    adc_values[ch] = (ADRESH << 8) | ADRESL;
}

What will be the content of adc_values after this loop?

medium

A. Array with zeros because ADC is not started

B. Array with ADC readings from channels 0, 1, and 2

C. Array with same value repeated 3 times

D. Compilation error due to wrong bit operations

Solution

1. Step 1: Analyze loop operation

   The loop runs for ch = 0 to 2, selecting each ADC channel and starting conversion.

2. Step 2: Understand ADC reading storage

   After conversion, the 10-bit ADC result is stored in adc_values[ch] for each channel.

3. Final Answer:

   Array with ADC readings from channels 0, 1, and 2 -> Option B

4. Quick Check:

   Loop reads channels 0-2 storing results in array [OK]

Hint: Loop reads and stores ADC values channel-wise [OK]

Common Mistakes:

• Assuming ADC conversion never starts
• Thinking all values are identical
• Misreading bitwise operations as errors

4.

Identify the error in this multi-channel ADC scanning code snippet:

for(int i = 0; i < 3; i++) {
    ADCON0 = (i << 2); // Select channel
    ADCON0 |= 0x01; // Turn on ADC
    ADCON0 |= 0x02; // Start conversion
    while(ADCON0 & 0x02);
    adc_results[i] = (ADRESH << 8) | ADRESL;
}

medium

A. The ADC result is stored incorrectly

B. The conversion start bit is never set

C. ADCON0 is overwritten before turning on ADC, losing previous bits

D. The loop runs one time too many

Solution

1. Step 1: Check ADCON0 assignment

   ADCON0 is assigned with (i << 2), which clears other bits including ADC enable.

2. Step 2: Understand bitwise OR usage

   Turning on ADC with |= 0x01 works, but previous bits are lost due to overwrite.

3. Final Answer:

   ADCON0 is overwritten before turning on ADC, losing previous bits -> Option C

4. Quick Check:

   Overwriting ADCON0 clears important bits [OK]

Hint: Use |= to set bits, not = to overwrite [OK]

Common Mistakes:

• Ignoring that ADCON0 bits get reset
• Thinking start bit is not set
• Miscounting loop iterations
• Misunderstanding ADC result storage

5.

You want to scan 4 analog sensors using a microcontroller ADC that supports hardware scanning. Which approach best improves efficiency?

// Option 1: Manually switch channels in software loop
// Option 2: Enable hardware scan mode and read results from buffer
// Option 3: Use single channel repeatedly
// Option 4: Use digital inputs instead

hard

A. Use hardware scan mode and read results from buffer

B. Manually switch channels in software loop

C. Use single channel repeatedly with delays

D. Use digital inputs instead of ADC

Solution

1. Step 1: Compare manual vs hardware scanning

   Manual switching requires CPU cycles and delays; hardware scan automates channel switching.

2. Step 2: Identify efficiency gain

   Hardware scan mode reads multiple channels automatically, storing results in buffer for quick access.

3. Step 3: Evaluate other options

   Using single channel repeatedly or digital inputs does not meet multi-channel analog reading needs efficiently.

4. Final Answer:

   Use hardware scan mode and read results from buffer -> Option A

5. Quick Check:

   Hardware scan mode = efficient multi-channel ADC reading [OK]

Hint: Hardware scan automates multi-channel ADC reading [OK]

Common Mistakes:

• Choosing manual switching which wastes CPU time
• Using single channel repeatedly causing delays
• Confusing digital inputs with analog ADC inputs