Digital to Analog Converter

• If a converter has 3 inputs then 8 input combinations are possible• If the full-scale analog voltage is 1v , then smallest unit is 1/8 v• If the input is increment by 1 then analog output increased by 1/8 v

• MP first write the data into the latch and it supply to converter• The latch is interfaced in I/O mapped I/O

• Because 8 address lines are used and IOW signal is used for writing• ADC converter receive digital data from latch and give corresponding

Analog current• That current is converted to voltage by Op-Amp• The 1408 is an 8 bit D/A converter• It’s full-scale current is 2 mA • Full-scale current is determined by resister R14 and Vref • Then smallest unit is 2mA/256= 7.81 μA• That is if digital input is incremented by 1 then analog input is

incremented by 7.18 μA• Io = Vref/ R14 X ( A1/2 + A2/4 + A3/8 + A4/16 +A5/32 + A6/64 + A7/128

+ A8/256)• VO = IO X 5k

Digital to Anolog converter

• ADC has one analog input and three digital output• So 8 outputs are possible • If analog input is incremented by 1/8 v the digital output will be

incremented by 1• It need some time for this conversion called conversion time• This is defined as the total time required to convert an analog signal into

its digital output

Successive Approximation A/D Converter

• When the analog input is applied, the successive approximation register generate 100

• Since it is higher value, controller instruct to decrement then it generate 010

• Since it is lower value, controller instruct to increment then successive approximation register generate 011 as correct value

• A/D is interfaced in I/O mapped I/O • So 8 address lines are used• IOW and IOR control signals are used• First MP send low to the START pin of A/D converter• ie send 0 to the address 82(H)• Then A/D converter start the conversion• MP continuously read the DR (Data Ready) signal • Ie read from the addres 81(H)• If the DR signal is low, MP will read the data from A/D converter• Ie from the address 80(H)