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ADC

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Analog-to-Digital Converter (ADC) in LPC2148

LPC2148 ADC Basics

  • Number of ADCs: Two 10-bit ADCs - ADC0 and ADC1.
  • Channels:
    • ADC0: 6 channels.
    • ADC1: 8 channels.
  • Conversion Technique: Successive Approximation (iterative narrowing down of value range).
  • Clock Requirement: ADC clock frequency must be 4.5 MHz or less, adjustable via a clock divider.
  • Voltage Range: ADCs operate between 0V and a reference voltage (VREF), typically 3V, but not exceeding the microcontroller’s supply voltage (VDDA).

Mermaid Diagram: ADC Features

graph LR
    A("LPC2148 ADC")
    B("2x 10-bit ADCs")
    C("ADC0: 6 Channels")
    D("ADC1: 8 Channels")
    E("Successive Approximation")
    F("Clk <= 4.5 MHz")

    A --> B
    B --> C
    B --> D
    A --> E
    A --> F

Key ADC Concepts

  1. Channels:
    • Dedicated input paths for specific analog signals.
    • Useful for connecting various sensors.
  2. Clock:
    • Drives the ADC operation.
    • Requires careful configuration to meet speed and accuracy demands.
  3. Precision:
    • 10-bit resolution translates to 1024 discrete levels.
    • Ensures fine-grained signal representation.

Registers Overview

Important Registers

  1. ADOCR (ADC Control Register):

    • Configures ADC operation.
    • Key Fields:
      • SEL (Bits 7:0): Selects the ADC channel.
      • CLKDIV (Bits 15:8): Sets clock division to adjust ADC clock frequency.
      • BURST (Bit 16): Enables repeated conversions without software intervention.
      • CLKS (Bits 19:17): Configures the number of clocks and precision.
      • PDN (Bit 21): Powers up the ADC.
      • START (Bits 26:24): Controls conversion start triggers.
      • EDGE (Bit 27): Defines trigger edge for external signals.

  2. ADGDR (ADC Global Data Register):

    • Stores the result of the most recent conversion.
    • Key Fields:
      • DONE (Bit 31): Indicates conversion completion.
      • RESULT (Bits 15:6): Holds the 10-bit conversion value.

  3. ADSTAT (ADC Status Register):

    • Reflects status flags for all channels.
    • Key Fields:
      • DONE7:0: Conversion completion flags for each channel.
      • OVERRUN7:0: Indicates data loss due to overwritten results.
      • ADINT: Signals interrupt for completed conversions.

  4. ADINTEN (ADC Interrupt Enable Register):

    • Enables interrupt generation for specific channels.
    • Key Fields:
      • EN7:0: Enables interrupts for individual channels.
      • ADGINTEN: Enables global interrupt for any channel completion.

  5. ADxDR (ADC Data Registers):

    • Individual registers for each channel.
    • Key Fields:
      • RESULT (Bits 15:6): Stores the conversion result.
      • DONE (Bit 31): Flags conversion completion for the specific channel.

Registers Names

graph LR
    R("ADC Registers")
    CR("ADxCR: Control Register")
    GDR("ADxGDR: Global Data Register")
    STAT("ADxSTAT: Status Register")
    INTEN("ADxINTEN: Interrupt Enable Register")
    CHDR("ADxDRy: Channel Data Registers")

    R --> CR
    R --> GDR
    R --> STAT
    R --> INTEN
    R --> CHDR

Summary of Key Configurations

  • Configure ADOCR for:
    • Channel selection.
    • ADC clock setup.
    • Enabling burst or software-controlled modes.
  • Use ADGDR and ADxDR to read conversion results.
  • Leverage ADSTAT for monitoring channel statuses.
  • Enable interrupts via ADINTEN for efficient ADC event handling.

Missed Points

CLKS Bits (Bits 19:17)

  • These bits configure the number of clocks used for each conversion in burst mode and determine the accuracy of the conversion result.
  • Values:
    • 000: 11 clocks for 10-bit resolution.
    • 001: 10 clocks for 9-bit resolution.
    • 010: 9 clocks for 8-bit resolution.
    • 011: 8 clocks for 7-bit resolution.
    • 100: 7 clocks for 6-bit resolution.
    • 101: 6 clocks for 5-bit resolution.
    • 110: 5 clocks for 4-bit resolution.
    • 111: 4 clocks for 3-bit resolution.

START Bits (Bits 26:24)

  • Define how and when the ADC conversion process begins.
  • Values:
    • 000: No start; used when clearing power-down mode.
    • 001: Start conversion immediately.
    • 010 to 111: Start conversion triggered by external MAT or CAP signals (controlled by the EDGE bit).

These additional configurations enhance flexibility, allowing for tailored precision and trigger mechanisms in ADC operations.

Register Summary Table

RegisterDescriptionKey Fields
ADOCRADC Control RegisterSEL: Selects ADC channel, CLKDIV: Clock divider, BURST: Burst mode, CLKS: Conversion precision, PDN: Power, START: Trigger start, EDGE: Trigger edge
ADGDRADC Global Data RegisterDONE: Conversion complete, RESULT: 10-bit conversion result
ADSTATADC Status RegisterDONE7:0: Channel completion flags, OVERRUN7:0: Overrun indicators, ADINT: ADC interrupt flag
ADINTENADC Interrupt Enable RegisterEN7:0: Enable interrupts for channels, ADGINTEN: Enable global interrupt for ADC completion
ADxDRADC Individual Channel Data RegistersRESULT: 10-bit conversion result, DONE: Conversion completion flag

Code Example

example program to read an analog voltage using the LPC2148 microcontroller. The program converts an analog signal from ADC0.1 (pin P0.28) into a digital value and displays the equivalent voltage on an LCD.

#include <lpc214x.h>
#include <stdint.h>
#include "LCD-16x2-8bit.h"
#include <stdio.h>
#include <string.h>
 
int main(void) {
    uint32_t result;
    float voltage;
    char volt[18];
 
    // Initialize LCD
    LCD_Init();
 
    // Configure P0.28 as ADC0.1
    PINSEL1 = 0x01000000;  // Set P0.28 as AD0.1
 
    // Configure ADC Control Register
    AD0CR = 0x00200402;  // ADC operational, 10-bit, 11 clocks for conversion
 
    while(1) {
        // Start Conversion
        AD0CR |= (1 << 24);  // Start conversion
 
        // Wait for conversion to complete
        while (!(AD0GDR & 0x80000000));  // Check DONE bit
 
        // Read result
        result = (AD0GDR >> 6) & 0x3FF;  // Extract 10-bit result
 
        // Calculate voltage
        voltage = ((result / 1023.0) * 3.3);
 
        // Display voltage on LCD
        LCD_Command(0x80);  // Move cursor to first line
        sprintf(volt, "Voltage = %.2fV", voltage);
        LCD_String(volt);
 
        memset(volt, 0, 18);  // Clear the buffer
    }
 
    return 0;
}

This program demonstrates how to:

  • Set up the ADC input pin.
  • Configure the ADC Control Register.
  • Read the digital result and convert it back to voltage.
  • Display the result on an LCD.

General Steps for Programming ADC in LPC2148

The following steps outline the general process for setting up and using the Analog-to-Digital Converter (ADC) in LPC2148:

1. Configure the ADC Control Register (ADxCR)

  • Set up the required ADC channel using the SEL field.
  • Configure the ADC clock frequency using the CLKDIV field to ensure it does not exceed 4.5 MHz.
  • Adjust other parameters such as burst mode, resolution (via CLKS), and power settings.

2. Start the Conversion

  • Trigger the start of the A/D conversion by writing to the START bits in the ADxCR register.
  • Example: Setting START = 001 initiates an immediate conversion.

3. Monitor the DONE Bit

  • Check the DONE bit in the respective ADC Data Register (ADxDRy).
  • Wait for this bit to change from 0 to 1, indicating the conversion is complete.

4. Retrieve the ADC Result

  • Read the converted value from the RESULT field in ADxDRy.
  • Convert this digital value into an equivalent analog voltage if needed.
stateDiagram-v2
    [*] --> ConfigureADC : Initialize ADC
    note right of ConfigureADC
        • Set ADC Control Register (ADxCR)
        • Configure clock divisor
        • Enable ADC
    end note

    ConfigureADC --> SelectChannel : Choose Analog Channel
    note right of SelectChannel
        • Select specific input channel
        • Prepare for conversion
    end note

    SelectChannel --> StartConversion : Trigger Conversion
    note right of StartConversion
        • Write to START bits
        • Immediate or software trigger
        • Begin analog-to-digital conversion
    end note

    StartConversion --> MonitorStatus : Check Conversion Status
    note right of MonitorStatus
        • Poll DONE bit
        • Wait for conversion complete
        • Bit 31 in ADC Data Register
    end note

    MonitorStatus --> ReadResult : Extract Digital Value
    note right of ReadResult
        • Read ADC Data Register (ADxDRy)
        • Extract 10-bit result
        • Optional: Convert to voltage
    end note

    ReadResult --> [*] : Conversion Complete

Graph View

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