ADC interrupt-driven reading in Embedded C - Step-by-Step Execution

Concept Flow - ADC interrupt-driven reading

Start ADC Conversion

↓

ADC Conversion Complete?

No→Wait

Yes↓

ADC Interrupt Triggered

↓

Interrupt Service Routine (ISR)

↓

Read ADC Result

↓

Process or Store Result

↓

Restart ADC Conversion

↩Back to Start

The ADC starts conversion, waits until done, triggers an interrupt, ISR reads and processes the result, then restarts conversion.

Execution Sample

Embedded C

void ADC_ISR(void) {
  int adc_value = ADC_Read();
  process(adc_value);
  ADC_StartConversion();
}

This ISR reads the ADC value when conversion completes, processes it, and starts a new conversion.

Execution Table

Step	Event	ADC Conversion Status	ISR Called	ADC Value Read	Action Taken
1	ADC conversion started	In Progress	No	N/A	Waiting for conversion
2	ADC conversion complete	Complete	Yes	Value read from ADC	Process value and restart conversion
3	New ADC conversion started	In Progress	No	N/A	Waiting for next conversion
4	ADC conversion complete	Complete	Yes	New value read	Process value and restart conversion
Exit	Stop or power down	N/A	No	N/A	ADC conversions stopped

💡 ADC conversions stop when device powers down or ADC is disabled

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
adc_value	undefined	Value from first conversion	Value from second conversion	Last read value
ADC Conversion Status	Idle	Complete	Complete	Stopped or Idle

Key Moments - 3 Insights

Why does the ADC conversion start again inside the ISR?

Because after reading the ADC value in the ISR (see Step 2 in execution_table), we need to start a new conversion to keep reading fresh data continuously.

What triggers the ADC ISR to run?

The ADC hardware triggers the ISR automatically when the conversion completes (Step 2 and 4 in execution_table), so the CPU can read the result immediately.

Why don't we read the ADC value outside the ISR?

Reading inside the ISR ensures we get the value right after conversion finishes, avoiding delays or missed data, as shown in the execution_table steps.

Visual Quiz - 3 Questions

Look at the execution_table, what is the ADC Conversion Status at Step 1?

A Complete

B Idle

C In Progress

D Stopped

💡 Hint

Check the 'ADC Conversion Status' column at Step 1 in the execution_table.

At which step does the ISR read the ADC value?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look for 'ISR Called' and 'ADC Value Read' columns in execution_table.

If the ADC conversion never completes, what happens to the ISR calls?

A ISR is called repeatedly

B ISR is never called

C ISR is called once

D ISR calls happen randomly

💡 Hint

Refer to the 'ADC Conversion Complete?' decision in concept_flow and ISR trigger in execution_table.

Concept Snapshot

ADC interrupt-driven reading:
- Start ADC conversion
- Wait for conversion complete interrupt
- ISR reads ADC value
- Process value inside ISR
- Restart conversion for continuous reading

Full Transcript

This visual execution trace shows how ADC interrupt-driven reading works. The ADC starts conversion and waits until it finishes. When done, it triggers an interrupt. The interrupt service routine (ISR) runs, reads the ADC value, processes it, and starts a new conversion. Variables like adc_value update after each ISR call. This cycle repeats until ADC is stopped or powered down. Key points include starting conversion inside ISR and ISR triggering only after conversion completes.