14-09-2013, 02:09 PM
ADC DEVICE (0804)
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INTRODUCTION
Analog-to-digital converters are among the most widely used devices for data acquisition. Digital. Computers use binary (discrete) values, but in the physical world everything is analog (continuous). Temperature, pressure, humidity, and velocity are a few examples of physical quantities that we deal with every day. Physical quantity is converted to electrical (voltage, current) signals using a device called a transducer. Transducers are also referred to as sensors. Although there are sensors for temperature, velocity, pressure, light, and many other natural quantities, they produce an output that is voltage (or current). Therefore, we need an analog-to-digital converter to translate the analog signals to digital numbers so that the micro controller can read them.
FEATURES:
Compatible with 8080 μP derivatives—no interfacing logic needed - access time - 135 ns
Easy interface to all microprocessors, or operates “stand alone”
Differential analog voltage inputs
Logic inputs and outputs meet both MOS and TTL
Voltage level specifications
Works with 2.5V (LM336) voltage reference
On-chip clock generator
0V to 5V analog input voltage range with single 5V supply
No zero adjust required
0.3 standard width 20-pin DIP package
20-pin molded chip carrier or small outline package
FUNCTIONAL DESCRIPTION:
The ADC0804 IC is an analog-to-digital converter in the family of the ADC800 series from National Semiconductors. It works with 5V and as a resolution of 8 bits in addition to resolution; conversion time is another major factor in judging an ADC. Conversion time is defined as the time it takes the ADC to convert the analog input to a digital (binary) number. In the ADC 0804, the conversion time varies depending on the clocking signals apply to the CLK R and CLK IN pins, but it cannot be faster than 110 micro seconds.
INTR:
This is an output pin and is active low. It is a normally high pin and when the conversion is finished, it goes low to signal the CPU that the converted data is ready t be picked up. After INTR goes low, we make CS=0 and send a high to low pulse to the RD pin t get the data out of the ADC 0804 chip.
ANALOG AND DIGITAL GROUND
These are the input pins providing the ground for both analog signal and digital signal and the digital signal. Analog ground is connected to the ground and of the analog Vin while digital ground is connected to the ground of Vcc pin. The reason that we have two ground pins is to isolate the analog vin signal from transient voltages caused by digital switching of the digital data output. D0-D7. Such isolation contributes to the accuracy of digital data output
1. Make CS=0 and send a low to high pulse to pin WR to start the conversion.
2. Keep monitoring the INTR pin. If INTR is low, low, the conversion is finished and we can go the next step. If INTR is high, keep polling until goes low.
3. After the INTR has become low, we make CS=0 and send a high to low pulse to the RD pin to get the data out of the ADC 0804 IC chip.