lecNew-13-ADCEx

lecNew-13-ADCEx - WPI ECE2801 Foundations of Embedded...

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WPI ECE2801 Foundations of Embedded Computer Systems Lecture 13: ADC Example
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EE2801: Foundations of Embedded Systems Lecture 13 Review: ADC12 Single 12 bit Analog-to-Digital Converter with built in Sample and Hold Can accept any of 8 (external) analog input signals or 4 internal analog inputs Analog inputs A0-A7 use same pins as Port 6! To select those pins for ADC analog input P6SEL bits =1. Selectable voltage references (V ref + and V ref- ) “One-shot” or continuous operation Single input channel or sequence of input channels 16 conversion result storage registers (each with its own control register)
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ADC Accuracy Ex. A simple digital current meter might measure current by measuring the voltage across a small sensing resistor. Can we use the ADC12 to measure across the range 0 to 1mA accuracy? How about 0.1 mA accuracy? EE2801: Foundations of Embedded Systems Lecture 13 V sens =R sens * i Set gain G so that 2.5V maps to 1A. Resolution To measure to .1mA, need to reduce the full scale range. Set gain G to map FSR to 2.5 V. (This is why a digital volt meter has different scales. ) mV V 61 . 4096 5 . 2 mA A 244 . 4096 0 . 1 A FSR FSR mA mA mA 4096 . 0 4096 1 . 1 . 1 .
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EE2801: Foundations of Embedded Systems Lecture 13 ADC12 Control Register ADC12CTL0 controls the following options Sample and Hold time (SHT1x and SHT0x) Multiple sample conversion method (MSC) Reference Voltages (REF2_5V and REF_ON) ADC12ON bit Enable and start conversion (ENC and ADC12SC) Overflow/Conversion time interrupt enables (ADC120VIE and ADC12TOVIE) ADC12 conversion core configured using ADC12CTL0 and ADC12CTL1 .
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lecNew-13-ADCEx - WPI ECE2801 Foundations of Embedded...

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