Adc0809 working principle diagram and program flow chart

ADC0809 is a CMOS-based 8-channel, 8-bit successive approximation analog-to-digital converter (ADC) manufactured by Texas Instruments. It features an internal 8-channel multiplexer that allows it to select and convert one of the eight analog input signals at a time, based on the address code provided. This device is commonly used in microcontroller-based systems for data acquisition tasks. The ADC0809 operates with a unipolar input signal ranging from 0 to 5 volts. If the input signal is too small, it must be amplified before being applied to the ADC. Additionally, the analog input should remain stable during the conversion process. If the signal changes rapidly, a sample-and-hold circuit should be added before the ADC to ensure accurate conversion. The ADC0809 uses several control lines for operation: - **ALE (Address Latch Enable)**: A high signal on this line latches the address inputs (A, B, C), which determine the selected channel for conversion. - **ST (Start Conversion)**: A rising edge on this line initiates the conversion process. - **EOC (End of Conversion)**: This signal goes high when the conversion is complete. - **OE (Output Enable)**: When set high, this enables the output of the converted digital data. - **CLK (Clock Input)**: An external clock signal, typically 500 kHz, is required for the ADC to function properly. - **VREF(+), VREF(-)**: These are the reference voltage inputs that define the full-scale range of the ADC. The ADC0809 has 11 digital output lines (D7-D0) that provide the converted digital value. The address lines A, B, and C are used to select the appropriate analog input channel from IN0 to IN7. The channel selection is determined by the binary combination of these three lines. In terms of application, the ADC0809 can be directly connected to a microcontroller like the AT89S51 due to its built-in output latches. To use it effectively, the following steps are generally followed: 1. Initialize the ST and OE signals to low. 2. Send the desired channel address to the A, B, and C pins. 3. Apply a positive pulse of at least 100 ns to the ST pin to start the conversion. 4. Monitor the EOC signal to determine when the conversion is complete. 5. Once EOC is high, set OE to high to enable the output of the converted data. The ADC0809 operates in a pulse-start mode, where the conversion starts after a falling edge on the START signal. After 10 microseconds, the EOC signal becomes active, indicating that the conversion is complete. The microcontroller can either poll the EOC signal or use an interrupt to read the converted data. Alternatively, a delay can be introduced after starting the ADC to allow the conversion to finish before reading the output. A typical program flow for using the ADC0809 involves initializing the hardware, selecting the channel, triggering the conversion, waiting for completion, and then reading the digital output. This process ensures reliable and accurate analog-to-digital conversion in real-time applications.

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