ADC 0808/0809 - Microprocessors and Microcontrollers - Computer Science Engineering (CSE) PDF Download

ADC 0808/0809:

• The analog to digital converter chips 0808 and 0809 are 8-bit CMOS, successive approximation converters. This technique is one of the fast techniques for analog to digital conversion. The conversion delay is 100µs at a clock frequency of 640 KHz, which is quite low as compared to other converters. These converters do not need any external zero or full scale adjustments as they are already taken care of by internal circuits.
• These converters internally have a 3:8 analog multiplexer so that at a time eight different analog conversion by using address lines - ADD A, ADD B, ADD C, as shown. Using these address inputs, multichannel data acquisition system can be designed using a single ADC. The CPU may drive these lines using output port lines in case of multichannel applications. In case of single input applications, these may be hardwired to select the proper input.
•  There are unipolar analog to digital converters, i.e. they are able to convert only positive analog input voltage to their digital equivalent. These chips do not contain any internal sample and hold circuit.
• If one needs a sample and hold circuit for the conversion of fast signal into equivalent digital quantities, it has to be externally connected at each of the analog inputs.

 Fig (1) and Fig (2) show the block diagrams and pin diagrams for ADC 0808/0809.

Fig.1 Block Diagram of ADC 0808/0809

Fig.2 Pin Diagram of ADC 0808/0809

Some Electrical Specifications Of The ADC 0808/0809 Are Given In Table.2.

Table.2

The Timing Diagram Of Different Signals Of Adc0808 Is Shown In Fig.3

Fig.3 Timing Diagram Of ADC 0808.