The analog to digital Converter chips 0808 and 0809 are 8-bit CMOS devices with an 8-channel multiplexer.
These devices are also designed to operate from common microprocessor control buses, with tri-state output latches driving the data bus.
Features
8-bit successive approximation ADC
Easy interface to all microprocessors.
It operates on single 5 V DC or analog span
Adjusted voltage reference.
No zero or full scale adjust required.
0V to 5V input range with single 5V power supply.
Outputs meet TTL voltage level specifications.
Operation
The analog to Digital Converter chips 0808 / 0809 are 8-bit CMOS successive approximation converters.
Successive approximation technique is one of the fast technique for analog to digital conversion.
The conversion delay is 100 μs at a clock frequency of 640kHz, which is quite low as compared to other converters.
These converters internally have 3: 8 analog multiplexer so that, at a time eight different analog inputs can be connected to the chips.
Out of these eight inputs only one can be selected for conversion by using address lines ADD A, ADD B and ADD C as shown.
Using these address inputs, multichannel data acquisition systems can be designed using a simple ADC.
The CPU may drive these lines using output port lines in case of multichannel applications.
In case of single channel application, there may be hard wired to select the proper input.
Interfacing ADC with 8085 Microprocessor
To interface the ADC with 8085, we need 8255 Programmable Peripheral Interface chip with it.
Let us see the circuit diagram of connecting 8085, 8255 and the ADC converter.
The Port A of 8255 chip is used as the input port. The PC7 pin of Port Cupper is connected to the End of Conversion (EOC) Pin of the analog to digital converter.
The PC2-0 lines are connected to three address pins of this chip to select input channels.
The PC3 pin is connected to the Start of Conversion (SOC) pin and ALE pin of ADC 0808/0809.
This port is also used as input port.
The Clower port is used as output port.
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