Implementing a DAC0832 to Output a Sawtooth Wave – Understanding Digital to Analog Conversion from Scratch

Today we will implement an interesting case: using the DAC0832 to output a sawtooth wave. Through this case, not only will we learn the basic principles of DACs, but we will also master the methods for waveform generation.

Introduction to DAC0832

The DAC0832 is an 8-bit digital-to-analog conversion chip. For example, it acts like a “tuner” that can output a corresponding analog voltage based on the digital signal input (0-255). Key features include:

• • 8-bit resolution
• • Parallel data input
• • Dual-buffer structure
• • Short setup time (1μs)

Hardware Connection Diagram

                     ┌─────────────┐
                     │   DAC0832   │
    Microcontroller  │             │
P1.0 ─────────────→ │D0       OUT │──────→ Oscilloscope
P1.1 ─────────────→ │D1      VREF │←──── +5V
P1.2 ─────────────→ │D2       GND │──────→ GND
P1.3 ─────────────→ │D3       CS  │←──── P3.0
P1.4 ─────────────→ │D4       WR1 │←──── P3.1
P1.5 ─────────────→ │D5       WR2 │←──── P3.2
P1.6 ─────────────→ │D6      XFER │←──── P3.3
P1.7 ─────────────→ │D7       ILE │←──── P3.4
                     └─────────────┘

Key Code Implementation

/* DAC0832 Write Data Function */
void DAC0832_Write(unsigned char dat)
{
    // Set data
    P1 = dat;      // Data line connected to P1 port
    
    // Timing control
    DAC_CS = 0;    // Chip select enabled
    DAC_WR1 = 0;   // Write signal
    DAC_WR2 = 0;
    
    // Delay to maintain stability
    Delay_us(1);
    
    // Complete writing
    DAC_WR1 = 1;
    DAC_WR2 = 1;
    DAC_CS = 1;
}

/* Main program to generate sawtooth wave */
void main()
{
    unsigned char i;
    
    // Initialize IO ports
    P1 = 0xFF;     // Initialize data port
    P3 = 0xFF;     // Initialize control port
    
    while(1)
    {
        // Output increasing voltage to form the rising edge of the sawtooth wave
        for(i = 0; i < 255; i++)
        {
            DAC0832_Write(i);
            Delay_us(20);    // Adjusting delay can change waveform frequency
        }
        
        // Voltage jumps to minimum value to form the falling edge of the sawtooth wave
        DAC0832_Write(0);
    }
}

Waveform Parameter Calculation

Assuming a delay of 20μs for each data point:

1. 1. Single cycle time = 255 × 20μs ≈ 5.1ms
2. 2. Waveform frequency ≈ 196Hz
3. 3. Voltage increment = 5V ÷ 255 ≈ 19.6mV/step

Precautions

1. 1. Hardware Considerations:

• • Reference voltage must be stable, recommended to use a reference source
• • It’s best to add an op-amp buffer stage at the output
• • Analog parts should be partitioned separately in PCB layout

• • Strictly adhere to timing requirements
• • Consider the sampling theorem, do not set the waveform frequency too high
• • Data updates should be uniform to avoid jitter

Common Issues and Solutions

1. 1. Waveform Distortion:

• • Check the stability of the reference voltage
• • Confirm whether the timing is correct
• • Observe if the ground line is clean

• • Increase decoupling capacitors
• • Optimize wiring
• • Check if the clock is accurate

Optimization Solutions

1. 1. Use a timer to control the update rate:

/* Use a timer to precisely control the update interval */
void Timer0_Init(void)
{
    TMOD &= 0xF0;
    TMOD |= 0x01;    // 16-bit timer mode
    TH0 = 0xFF;      // 20us timer value
    TL0 = 0xB1;
    ET0 = 1;         // Enable timer interrupt
    TR0 = 1;         // Start timer
}

/* Timer interrupt service function */
void Timer0_ISR(void) interrupt 1
{
    static unsigned char dac_value = 0;
    
    TH0 = 0xFF;      // Reload timer value
    TL0 = 0xB1;
    
    DAC0832_Write(dac_value++);  // Update DAC output
}

1. 2. Output buffer stage design:

DAC output ──┳──────┐
          ┃      │
         ███     └──┐
         ███ 1K    ─┴─
          ┃        ─┬─ 0.1μF
          ┃         │
         GND       GND

Extended Exercises

1. 1. Generate other waveforms:

• • Triangle wave
• • Step wave
• • Sine wave

• • Adjustable frequency
• • Adjustable amplitude
• • Waveform switching

Experience Sharing

In practical engineering applications, DAC outputs often encounter interference issues. Solutions include:

1. 1. Separate wiring for analog ground and digital ground, single-point grounding
2. 2. Key signal traces should avoid high-frequency interference sources
3. 3. Use opto-isolation when necessary

The most important experience is: digital-to-analog conversion circuits must pay attention to grounding issues, as poor ground design can lead to severe output distortion.