FMA Unit 5.6 Interfacing ADC to 8051

ANALOG TO DIGITAL CONVERTER

ADC0808/ADC0809 is an 8 channel 8-bit analog to digital converter.

Conversion Delay

Time taken by the ADC from the Active Edge of Start of Conversion (SOC) pulse till the Active Edge of (Start of Conversion) EOC pulse.

Algorithm:

·        Ensure the stability of anolog input applied to ADC.

·        Send the SOC pulse to ADC.

·        Read EOC signal to mark the end of the conversion process.

·        Read Digital output of the ADC as equivalent digital output.

Pin Configuration of ADC 0808

     ·        Analog Input (IN0 to IN7)

These pins are eight different analog input. Each of these inputs is converted to an 8-bit equivalent digital one by one not all at a time.

     ·        Address pins (ADD A, ADD B, ADD C)

These pins select input of the eight analog input for A to D conversion.

Address			Analog Input
C	B	A
0	0	0	IN 0
0	0	1	IN 1
0	1	0	IN 2
0	1	1	IN 3
1	0	0	IN 4
1	0	1	IN 5
1	1	0	IN 6
1	1	1	IN 7

     ·        ALE (Address Latch enable)

This pin is use to enable the address latch which is store the addresses on the line A, B, C

     ·        Output Enable

This pin is use to enable the digital output on the output lines.

     ·        2-1 to 2-8 (Digital Outputs)

These pins are used to provide digital outputs. 2^-1 represents the MSB and 2^-8 represents the LSB.

     ·        SOC (Start of Conversion)

To enable the start input to begin the A to D conversion. A pulse is to be given on SOC pin to start conversion.

     ·        EOC (End of conversion)

The end of the conversion is indicated by EOC output.

     ·        Vcc

This pin is used to provide supply of  5 V.

     ·        GND

This pin is used to provide ground to the supply

     ·        Vref ⁽⁺⁾ and Vref ^(-) (Reference voltages)

These pins are used to provide positive reference voltage or negative reference voltage depending on the desired polarity of reference voltage.

Interfacing ADC 0808 to 8051

     ·        ADC 0808 has eight input channels. Hence in order to select an input channel, it            essential to send 3 bit address on ADD C, ADD B, ADD A inputs.

     ·        The address of the desire channel is sent to the address input through port pins                P2.0, P2.1 and P2.2.

     ·        After 50 nSec the address must be latched. It can obtained by sending ALE signals.

     ·        After 2.5 µSec, SOC must be high and then low to start to start conversion.

     ·        To indiacate the end of the conversion EOC must be activated.

     ·        The 8051 pins P2.6 and P2.7 are connected to SOC and EOC pins of ADC 0808.

     ·        After the conversion is over, 8 bit digital data is present on D0 to D7 lines.                ·    8051 accept this 8-bit converted digital data through port 1.