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8/3/2019 Presentation Gani

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DACINERFACING


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DAC PRINCIPLE

To convert the digital signal to analogsignal a Digital-to-Analog Converter (DAC)has to be employed.

The DAC will accept a digital (binary) inputand convert to analog voltage or current.

Every DAC will have "n" input lines and an

analog output. The DAC require a reference analog voltage

(Vref) or current (Iref) source.


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CONTD.

The smallest possible analog value that can berepresented by the n-bit binary code is calledresolution.

The resolution of DAC with n-bit binary input is

1/2nof reference analog value Every analog output will be a multiple of the

resolution.

For example, consider an 8-bit DAC withreference analog voltage of 5 volts. The analogvalues for all possible digital input are as shown.


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CONVERSION TABLE :


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PIN DIAGRAM OF DAC0800


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EXPLANATION:

The DAC0800 is an 8-bit, high speed, current outputDAC with a typical settling time (conversion time) of100 ns.

It produces complementary current output, whichcan be converted to voltage by using simple resistorload.

The DAC0800 require a positive and a negative supplyvoltage in the range of 5V to 18V.

The DAC0800 is available as a 16-pin IC in DIP


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INTERNAL BLOC DIAG


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DAC 0800 with I to v conv..


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Contd

The reference voltage and the digital input will

decide the analog output current, which can beconverted to a voltage by simply connecting aresistor to output terminal or by using an op-ampI to V converter.


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Interfacing DAC0-800 with

8085 microprocessor


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CONTD.. The DAC0800 is interfaced using an 8-bit latch

74LS273 to the system bus

The 3-to-8 decoder 74LS 138 is used to generatechip select signals for I/O devices.

The address lines A4, A5 and A6 are used asinput to decoder.

The address line A7 and the control signal IO/M(low) are used as enable for decoder.


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Contd.. The decoder will generate eight chip select signals

and in this the signal IOCS-7 is used as enable forlatch of DAC.

The I/O address of the DAC is shown in table:


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In order to convert a digital data toanalog value, the processor has to

load the data to latch. The latch will hold the previous data

until next data is loaded.

The DAC will take definite time toconvert the data. The software shouldtake care of loading successive dataonly after the conversion time.

The DAC 0800 produces a currentoutput, which is converted to voltageoutput using Ito V converter

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