INTERFACING ADC USING 8051 MICROCONTROLLERIn this article you will learn how to interface, analog to digital converter with 8051 microcontroller. Unlike, pic microcontroller, Arduino and avr microcontroller, 8051 microcontroller do not have built in ADC.  if we want to interface any sensor with 8051 microcontroller, we have to use external ADC. For example, you want to measure temperature with 8051 microcontroller and you are using LM35 temperature sensor to measure temperature. LM35 temperature sensor gives output in the form of analog voltage. So we need to use analog to digital converter. We use Analogue to digital convertor (ADC) to convert the analogue signal into digital form. Analogue signal can be the output of some sensor. And then the data in digital format can then be used for further processing by the digital processors. Now in this tutorial we will learn about ADC 0804 and its interfacing using 8051 microcontroller.


Its main features are given below:

  • 8 bit resolution
  • Differential analogue voltage inputs
  • 0-5V input voltage range
  • No zero adjustment
  • Built-in clock generator
  • Voltage at Vref/2 (pin9) can be externally adjusted to convert smaller input voltage spans to full 8 bit resolution.


Resolution refers to the conversion of an analog voltage to a digital value. It indicates the number of discrete values that an ADC can produce over the range of analog values. The values are usually stored electronically in binary form, so the resolution is usually expressed in bits.


It is the voltage difference between one digital level and the next level that can be measured by ADC. In a 4-bit converter, an input of 1 Volt produce an output of 0001, then the step size is 1 Volt. 0 volts is always considered 0000. Distortion in the signal can be reduced by decreasing the step size to 0.5 voltsbut it lowers the maximum input reading. Ife we are using smaller step size, higher bit converter is needed to have maximum voltage.

ADC0804 is a single channel analog to digital convertor. It takes only one analog signal. It has 8 bit resolution. Other ADC can have n bit resolution and n can be 8,10,12,16 or 24 bits. If ADC has higher resolution, it gives smaller step size.If ADC has 8 bit resolution, input voltage span is 0-5V and the step size is 19.53mV (5V/255). In this situation we called Vref/2 as left open.

PIN DIAGRAM:ADC0804 interfacing with 8051 microcontroller


Pin description of ADC0804 is given below:

CS:                  Chip Select
It is an active low pin and is used to activate ADC0804

RD:                 Read
It is an input pin and is active low. ADC stores the result in an internal register after conversion of analog data. This pin helps to get the data out of the ADC0804.
When CS=0, high to low pulse is given to RD pin, then digital output comes on the pins D0-D7

WR:                Write
It is an input pin and is active low which is used to initiate the ADC to start the conversion process.
When CS=0, WR makes a low to high transition, then ADC starts the conversion process.

CLK IN:        Clock IN
This is an input pin which is connected to an external clock source.

INTR:             Interrupt
This is an output pin and is active low.When the conversion is over, this pin goes low.

Vin+:              Analog Input
Analog input to ADC.

Vin-:               Analog Input.
Analog input connected to ground.

AGND:           Analog Ground
Connected to ground.

Vref/2:            Reference Voltage
Used to set the reference voltage. Default reference voltage is 5V when not connected.Step size can be reduced by using this pin.

DGND:           Digital Ground
Connected to ground.

D7-D0:            Output Data Bits

Output bits of binary data.

CLKR:           Clock Reset
To reset the clock.

Vcc:                Positive Supply
Power supply of ADC.


  • Firstly make CS=0.
  • Send a low to high pulse to WR pin to start the conversion.
  • Keep checking the INTR pin.

INTR = 1, if conversion is not finished, poll until it is finished

INTR = 0, if conversion is finished.

  • If conversion is finished (INTR=0), Ensure CS=0
  • Then, send a high to low pulse to RD pin to read the data from the ADC.
  • If we connect CS of ADC to ground, then there will be no need to make or ensure it to zero.


As we know that microcontroller willprovide control signals to the ADC. Its main connections are as follow:ADC0804 conversion steps

  • CS pin of ADC is connected to ground.
  • 5of MCU is connected to WR of ADC0804.
  • 6 of MCU is connected to RD of ADC0804.
  • 4 of MCU is connected to INTR of ADC0804.
  • Output is demonstrated through LEDs which are connected between the Data out pins of ADC0804 and port 0 of 8051 microcontroller.
  • Input voltage from the preset is varied and the output of ADC varies.


ADC interfacing with 8051 microcontroller simulation results


Port 1 is used as input port and port 0 is used as output port. Potentiometer is used to adjust the voltage.  If the analogue input voltage is 5V then all LEDs will glow indicating 11111111 in binary which is the equivalent of 255 in decimal. If the voltage is zero, no LED will glow.

When full voltage given:(Output =11111111)ADC interfacing with 8051 microcontroller full voltage

When half voltage given:ADC interfacing with 8051 microcontroller half voltage input 

When zerovoltage given:(Output = 00000000)ADC interfacing with 8051 microcontroller zero voltage



#define input P1                                              //Input port (read values of ADC)

#define output P0                                           // Output port (connected to LED's)

void delay(unsigned intmsec );


sbitwr= P3^5;                                                    // Write pin.

sbitrd= P3^6;                                                     // Read pin.

sbitintr= P3^4;                                   // Interrupt pin.
void main()


input=0xff;                                                         // Declare port 1 as input port.

output=0x00;                                                     // Declare port 0 as output port.






void delay(unsigned intmsec )                   // Delay function


inti,j ;


for(j=0; j<1275; j++);

voidadc()                                                             // Reading values from ADC and display on the LED's












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