Lec11 - EE319K IntroductiontoMicrocontrollers...

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11-1 EE 319K Introduction to Microcontrollers Lecture 11: A/D Conversion and Lab 6 Read Book Sections 10.2 and 11.4
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Ramesh Yerraballi 11-2 A/D and D/A Conversion Basics Digitization :Amplitude and time quantizing T ime (s) 0 4 8 12 16 20 24 28 32 0 1 2 3 4 5 6 7 8 9 10 Continuous analog signal D iscrete digital signal
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Ramesh Yerraballi 11-3 Nyquist Theory If a signal is sampled at f s  then the digital samples only contain  frequency components  from 0 to (1/2)f s Conversely,  if the analog signal does contain frequency  components larger than (1/2)f s , then there will be an  aliasing   error. Aliasing is when the digital signal appears to have a different frequency  than the original analog signal.  Say, V(t) = A sin(2 π ft +  φ ) Nyquist theory says that if f s  is strictly greater than twice f, then  one can determine A f and  φ  from the digital samples. But if   f s  is less than or equal to 2f, then the apparent frequency,  as predicted by analyzing the digital samples, will be shifted to a  frequency between 0 and (1/2)f s
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Ramesh Yerraballi 11-4 .. Nyquist Theory Sampled Data -3 -2 -1 0 1 2 3 0 2 4 6 8 10 Time (ms) Sampled Data True Data A 1500 Hz sine wave is sampled at 1600 Hz.
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Ramesh Yerraballi 11-5 A/D and D/A Conversion Basics Range  of the system is the  maximum minus the minimum  values  Precision  of the system  defines the number of values  from which the amplitude of  the digital signal is selected.  (Alternatives)  Resolution  is the smallest  change in value that is  significant. Range = Precision x Resolution
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Ramesh Yerraballi 11-6 A/D Converter Example Analog to digital Converter  Analog input 0 ≤ V in  ≤ +5 Digital output 0 ≤  ATD0DR0  ≤ 1023 o Digital Output is about 1024*V in /5  o Or Digital Output is about 1023*V in /5  0 +5 0 1023 Analog Digital V in
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Ramesh Yerraballi 11-7 9S12 has 16 Analog Inputs AD1 AD0 One Control Register per ADC module:       ATD0CTL2 and ATD1CTL2
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Ramesh Yerraballi 11-8 Port AD0 Address Bit 7 6 5 4 3 2 1 Bit 0 Name $0082 AFFC AWAI ETRIGLE ETRIGP ETRIG ASCIE ASCIF ATD0CTL2 $0083 0 FIFO FRZ1 FRZ0 ATD0CTL3 $0084 SMP1 SMP0 PRS4 PRS3 PRS2 PRS1 PRS0 ATD0CTL4 $0085 DJM DSGN SCAN MULT 0 CC CB CA ATD0CTL5 $0086 SCF 0 ETORF FIFOR 0 CC2 CC1 CC0 ATD0STAT0 $008B CCF7 CCF6 CCF5 CCF4 CCF3 CCF2 CCF1 CCF0 ATD0STAT1 $008D Bit 7 6 5 4 3 2 1
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This note was uploaded on 01/25/2010 for the course EE 319K taught by Professor Bard during the Spring '08 term at University of Texas at Austin.

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Lec11 - EE319K IntroductiontoMicrocontrollers...

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