## ADC0803LCWM: Technical Overview The **ADC0803LCWM** is a widely used 8-bit CMOS successive approximation Analog-to-Digital Converter (ADC). It is designed to interface directly with microprocessors and operates on a single 5V power supply. ### 1. Key Technical Specifications | Parameter | Specification | |:---|:---| | **Resolution** | 8 Bits | | **Conversion Time** | 100 µs (typical) | | **Input Voltage Range** | 0V to 5V (Adjustable via $V_{ref}/2$) | | **Supply Voltage ($V_{cc}$)** | 4.5V to 6.3V | | **Interface** | Parallel (Tri-state outputs) | | **Package Type** | SOIC-20 (Wide Body) | | **Clock Source** | Internal or External | --- ### 2. Pin Descriptions and Functions The ADC0803LCWM features 20 pins. Below are the primary functional groups: #### Power and Ground - **$V_{cc}$ (Pin 20):** Positive power supply (+5V). - **AGND (Pin 8):** Analog ground; connect to the analog signal source ground. - **DGND (Pin 10):** Digital ground; connect to the system logic ground. #### Control Signals - **CS (Pin 1):** Chip Select. Must be LOW for the chip to be active. - **RD (Pin 2):** Read. When LOW, the output latches are enabled, and data is placed on the bus. - **WR (Pin 3):** Write. A high-to-low transition starts the conversion process. - **INTR (Pin 5):** Interrupt. Goes LOW when the conversion is complete. #### Analog Inputs - **Vin(+) & Vin(-) (Pins 6, 7):** Differential analog inputs. This allows for noise rejection and offset adjustments. - **$V_{ref}/2$ (Pin 9):** Reference voltage input. Setting this pin to 2.5V allows a full input range of 0-5V. #### Digital Outputs - **DB0 to DB7 (Pins 11-18):** 8-bit parallel digital data output. --- ### 3. Conversion Mechanism The ADC0803 uses the **Successive Approximation Register (SAR)** method. It compares the input voltage against a series of voltages generated by an internal DAC until it finds the closest digital match. #### Timing Sequence: 1. **Start:** The microprocessor pulls `CS` and `WR` LOW. 2. **Process:** The internal clock begins the SAR algorithm. 3. **End:** Once finished, the `INTR` pin goes LOW. 4. **Retrieve:** The microprocessor pulls `RD` LOW to read the 8-bit data from the `DB` pins. --- ### 4. Circuit Implementation (Example) To use the internal clock, a simple RC circuit is connected to pins 4 (CLK IN) and 19 (CLK R): ```text Clock Frequency (f) ≈ 1 / (1.1 * R * C) Typical values: R = 10kΩ, C = 150pF ``` ---