interfacing experiment adc

Experiment No. : 22 Title: Interfacing 8085 Microprocessor with Analog to Digital (ADC) Converter. Objective: 1. Interface an eight bit Analog to Digital Converter (ADC) to a 8085µP Kit . 2. Write assembly language program to calibrate the system so developed to measure unknown d.c. voltage. 3. Draw calibration curve between analog input voltage and ADC output. Theory of Analog to Digital Conversion: Principle of Operation: ADC to be use is ADC-0809 built by National Semiconductor. It is an eight bit converter capable of 10,000 conversions per second. It has eight analog inputs (IN0 – IN7) selected by a 3 line address system (three bits will determine one of eight possibilities.) The three address lines are ADD A, ADD B and ADD C. The selection of the Analog input line via the three address lines is not accomplished until the ALE (Address Latch Enable) line is pulsed. The converter is started with a pulse to the START line. It changes the state of the EOC (End Of Conversion) line when done with its conversion, and the data is sent out the data lines when OE (Output Enable) is low. The CLOCK line sets the speed with which this successive approximation converter works. It must be less than 1.25 Megahertz. The output code N for an arbitrary input are the integers within the range (for ADC 0809 range between 0 and 255): Features of ADC 0809 are ■ Easy interface to all microprocessors ■ Operates ratiometrically or with 5 V DC or analog span adjusted voltage reference ■ No zero or full-scale adjust required ■ 8-channel multiplexer with address logic ■ 0V to 5V input range with single 5V power supply ■ Outputs meet TTL voltage level specifications ■ Standard hermetic or molded 28-pin DIP package

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Interfacing Experiment ADC

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Experiment No. : 22

Title: Interfacing 8085 Microprocessor with Analog to Digital (ADC) Converter. Objective:

1. Interface an eight bit Analog to Digital Converter (ADC) to a 8085µP Kit .2. Write assembly language program to calibrate the system so developed to measure unknown d.c. voltage.3. Draw calibration curve between analog input voltage and ADC output.

Theory of Analog to Digital Conversion:

Principle of Operation: ADC to be use is ADC-0809 built by National Semiconductor. It

is an eight bit converter capable of 10,000 conversions per second. It has eight analog inputs (IN0 – IN7) selected by a 3 line address system (three bits will determine one of eight possibilities.) The three address lines are ADD A, ADD B and ADD C. The selection of the Analog input line via the three address lines is not accomplished until the ALE (Address Latch Enable) line is pulsed.

The converter is started with a pulse to the START line. It changes the state of the EOC (End Of Conversion) line when done with its conversion, and the data is sent out the data lines when OE (Output Enable) is low. The CLOCK line sets the speed with which this successive approximation converter works. It must be less than 1.25 Megahertz.

The output code N for an arbitrary input are the integers within the range (for ADC 0809 range between 0 and 255):

Features of ADC 0809 are■ Easy interface to all microprocessors■ Operates ratiometrically or with 5 VDC or analog span adjusted voltage reference■ No zero or full-scale adjust required■ 8-channel multiplexer with address logic■ 0V to 5V input range with single 5V power supply■ Outputs meet TTL voltage level specifications■ Standard hermetic or molded 28-pin DIP package■ 28-pin molded chip carrier package

Key Specifications■ Resolution : 8 Bits■ Single Supply : 5 VDC

■ Low Power : 15 mW■ Conversion Time : 100 µs