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ANSFA - E C E 4 1 7 5 A F in a l 1 2-1 0-0 8 SE V E N PR O...

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ECE 4175A Final 12-10-08 Page 1 of 3 High 111 SEVEN PROBLEMS Upper quarter 88 Open book, open notes Median 79 Lower quarter 74 Low 60 1. [ ] I have completed the CIOS course evaluation. [5%] [ ] I have not completed the CIOS course evaluation. 2. W e discussed how a 1-wire chip makes use of “parasitic power” obtained from the 1-wire data I/O line. DD The same thing can occur on a protoboard having an IC whose V power pin has inadvertently been left DD [15%] disconnected from the +3V coin cell but which does have an 0.1 : F capacitor connected between V and GND pins. The rest of the circuit on the protoboard is powered and has circuitry that drives inputs to the mis-wired IC. The IC seems to work intermittently. a. Given that this IC has internal overvoltage and undervoltage protection diodes on each of its inputs, draw a circuit showing the circumstances under which the chip obtains power and works. b. Explain what is going on and why the IC sometimes works and sometimes does not. If any input to the chip is high, the diode protect circuitry will charge the 0.1 : F capacitor to VDD minus the diode drop and the chip will work. If all inputs are low, the 0.1 : F capacitor will discharge toward 0V and at some point, the chip will cease to have enough supply voltage to work. 3. In class, I demonstrated the magnetic card reader. After reading the output with the PIC18LF4321 on the Qwik&Low board, the result was sent to a laptop whose display was projected for all to see. When the [15%] card was swiped at a “normal” or slow rate, we witnessed a repeatable output. However, a fast swipe could produce results that did not repeat. Assume that the interrupt handler in the 4321 did not make use of the parity bit associated with each character to detect errors.
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