Unformatted text preview: ME 461 Prelab #3
Due at the start of Lab #3
Suggested Reading: ADC10 chapter in MSP430x2xx user’s guide. National Semiconductor LM386 datasheet. Lab 3 manual. 1. Suppose you want to sample and convert the voltage provided from a source with output impedance of 5 kΩ. Compute the minimum sample‐hold time required to ensure an accurate ADC conversion on the MSP430F2272. 2. Now suppose the ADC conversion clock is running at 5 MHz. Write the configuration of the ADC10SHT bits in ADC10CTL0 that achieves the sample‐hold time from problem 1 without wasting unnecessary clock cycles. With this configuration, what is the theoretical maximum rate at which you could sample the ADC? 3. Write out the contents of the ADC10CTL0, ADC10CTL1, and ADC10AE registers for sampling channel A3 with the software trigger (ADC10SC), VCC and GND as the reference set, the sample‐hold time you found in problem 1, and interrupt enabled. Use the ADC10OSC clock source. 4. Write out the code you’d place in the Timer A ISR if you wanted to trigger ADC conversions every 5ms. Assume Timer A counts at 16MHz and TACCR0 = 16000. 5. What register contains the results of the analog‐to‐digital conversions? How precise is the result, assuming the only error is due to quantization (in percent)? Where in your program can you read this register and be sure it has a valid result? 6. Write the formula for converting from digital ADC reading to analog voltage. What is the digital reading that would result from sampling 1.25 volts using a reference set of VCC (≈3.6V) and GND? What is the analog voltage corresponding to a digital reading of 620? 7. Suppose you want to use the F2272’s ADC and the onboard temperature sensor to measure temperature. You sample the ADC in a room where a thermometer reads 25oC. The reading is consistently 1.25 V. What is the function that relates voltage to temperature for your specific device? You may use the published value for the slope. 8. If you obtained a reading of 2.5V after converting the temperature sensor voltage, what temperature would you surmise the chip is at? ME 461 1 Prelab #3 ...
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This note was uploaded on 11/07/2011 for the course ME 461 taught by Professor Staff during the Spring '08 term at University of Illinois, Urbana Champaign.
- Spring '08