The **ADE0804** (often associated with the industry-standard **ADC0804**) is an 8-bit CMOS successive-approximation Analog-to-Digital Converter (ADC). It is designed to interface directly with microprocessors by treating the conversion process like a memory read operation. --- ## 1. Key Specifications | Feature | Specification | | :--- | :--- | | **Resolution** | 8 Bits | | **Conversion Time** | 100 µs | | **Input Channels** | 1 Differential Channel | | **Operating Voltage** | 5V DC (typical) | | **Analog Input Range** | 0V to 5V (Adjustable via $V_{ref}/2$) | | **Package Type** | 20-pin DIP or SOIC | --- ## 2. Pin Configuration & Functions The device uses a 20-pin layout. Below are the primary functional groups: ### Control Pins * **CS (Chip Select):** Active LOW. Enables the chip for communication. * **RD (Read):** Active LOW. When low, the converted digital data is placed on the output pins. * **WR (Write):** Active LOW. A pulse starts the analog-to-digital conversion process. * **INTR (Interrupt):** Goes LOW when the conversion is complete and data is ready. ### Clock and Reference * **CLK IN / CLK R:** Used to set the internal clock frequency using an external RC circuit. * **Vref/2:** Allows setting a custom input range. For a 0-5V range, this is left open or set to 2.5V. ### Data Pins * **DB0 to DB7:** The 8-bit digital output bus. --- ## 3. Working Principle The ADE0804 operates on the **Successive Approximation Register (SAR)** principle. It compares the analog input voltage against a series of internally generated voltages to determine each bit of the 8-bit result, from Most Significant Bit (MSB) to Least Significant Bit (LSB). ### Typical Connection Code (Pseudocode logic) ```c // Process to read data from ADE0804 1. CS = 0; // Select the chip 2. WR = 0; // Start conversion 3. Delay(1us); // Wait for pulse width 4. WR = 1; // Conversion begins 5. While(INTR == 1); // Wait for INTR to go LOW (End of conversion) 6. RD = 0; // Enable output buffer 7. Data = P1; // Read 8-bit data from Port 8. RD = 1; // Disable buffer 9. CS = 1; // Deselect chip ``` --- ## 4. Application Circuit Diagram Components To make the ADE0804 functional, the following external components are usually required: 1. **Resistor (R) and Capacitor (C):** Connected to CLK R and CLK IN to define the conversion speed ($f \approx 1 / (1.1 \times R \times C)$). 2. **$V_{ref}/2$ Voltage Divider:** To set the span of the input (e.g., if $V_{ref}/2$ is 2V, the max input is 4V). 3. **Bypass Capacitor:** A 0.1µF capacitor across Vcc and GND to reduce noise.