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DEPT. ECE, EEL 4744 C FINAL EXAM Antonio A. Arroyo, Keith L. Doty NAME_________________________________________________________ SS#_________________________________________________________ UNIVERSITY OF FLORIDA DEPARTMENT OF ELECTRICAL ENGINEERING EEL4744C: MICROCOMPUTER APPLICATIONS Final Exam Instructions : Closed book, except for the 6811 Programming Reference Guide. No calculators. Answer all questions on the exam. If you need to use the back of the exam sheets indicate when doing so. For programming problems do not define the register equates.
15% 1. Answer the following laboratory related questions.
5% a) A PWM wave generated on OC3 of the 68HC11 drives a 12 volt DC motor after passing through the circuit below. OC3 drives pin 1 of a 7406. The output on pin 2 drives the DC motor controller which, in turn, drives the motor. Draw the output waveform produced on pin 2. Label all axes. Use Word 6.0c or later to view Macintosh picture. 4% b) Compute the duty cycle D of the input square wave. D = ________________________. Use Word 6.0c or later to view Macintosh picture.
DEPT. ECE, EEL 4744 C FINAL EXAM Antonio A. Arroyo, Keith L. Doty NAME_________________________________________________________ SS#_________________________________________________________ 6% c) Tachometer voltage of a DC motor equals Vin = 12 sin(2f t) for the circuit below. The zener is rated at 5 volts and [ increases, limits ] the voltage at the input of the 7406 inverter. The input 1K ohm resistor [ increases, limits ] the [ current through, voltage across ] the zener in order to protect it. Assume that no current flows through the input resistor until the zener conducts and that the inverter switches to ground when the input voltage is ≥ 2.4 volts and switches back to 5 volts when the input drops below 1 volt. If at t=0.1 seconds, the output just switches to ground, what is the period T of the output? Express T as a function of . (Hint: sin ≈ for small ). Show your work below. _T = _______________________
24% 2. A FHP trooper places a mechanical speed trap on one side of a two lane highway. Two
pressure hoses, lain across the road and separated by fixed, known distance d , generate a 10 ms pulse when depressed and will not generate another pulse until after the pressure is released. The hoses drive IC1 and IC2 as shown in the figure. 4% a) If a car passing over the speed trap has speed s and the IC2 leading edge occurs T seconds after the IC1 leading edge, derive a symbolic expression for s in terms of known parameters. s = __________________. 4%b) How many E-clock cycles E_VIOL does it take a car traveling at speed s = 120 kilometers/ hour to move 1 meter? Assume an 8 MHz crystal. E_VIOL = ______________________. 16% c) The highway is restricted to two axle cars d = 1 meter and s ≥ 120 kilometers/hour constitutes a speeding violation. Write an interrupt driven program that computes the speed of the currently passing car in E_SPEED (2 bytes) and its wheel base E_Axle (distance between axles) (2 bytes) of cars that passes over the hoses. These two variables can be expressed in E-clock counts. The constant E_VIOL in b) determines the maximum E-clock count that still indicates speeding. Your program also keeps a violation counter VCNT that accumulates the number of speeders. VCNT is cleared by a RESET. Data storage starts at Use Word 6.0c or later to view Macintosh picture. Use Word 6.0c or later to view Macintosh picture.
DEPT. ECE, EEL 4744 C FINAL EXAM Antonio A. Arroyo, Keith L. Doty NAME_________________________________________________________ SS#_________________________________________________________
16% 3. A robot illuminates objects with infrared light by means of an Infrared (IR) emitter. An IR
detector on the robot determines the distance to the object by measuring the amplitude of the IR light reflected by the object. The voltage response V of the IR detector obeys the equation V= ax^2 + bx + c , where 50mm ≤ x ≤ 300mm is the distance to the object reflecting the IR. 4% a) Determine the sensitivity S of this sensor when the object is at distance d. S = ________________ 2% b) Is IR detector linear? [Yes, No]. Explain. 4% c) An engineer measures the analog voltage output of the IR detector for an object at a fixed distance and constant illumination. Although nothing is changed during the experiments, she obtains the following A/D readings from the microcontroller: VAD = $6F,$68,$6D,$6A,$69, $68,$6C. How many bits resolution does the IR detector have at the distance measured? Explain. N = ___________________. 6% d) The constant c = 2.5 volts , but the constants a, b in the equation ax^2 + bx + c must be determined by experiments. What is the minimum number of measurements required to find a, b? _Min No. Experiments = ________________. After making the measurements, formulate (symbolically) the equations to be solved and the solution method. Do not actually solve the equations symbolically.
20% 4. Answer the following miscellaneous questions.
4% a) A program transmits two 7-bit ASCII capital letters XA with one start and one stop bit each. Draw the waveform transmitted. 3% b) According to the RS232-C protocol, an idle line is indicated by a voltage V in the range _____________________. A start bit must be in the voltage range ____________________. The probability of a false start is reduced by the SCI system by _______________________
DEPT. ECE, EEL 4744 C FINAL EXAM Antonio A. Arroyo, Keith L. Doty NAME_________________________________________________________ SS#_________________________________________________________
4% c) The SCI system is double buffered on transmit and receive. Explain how double buffering on the SCI works. Double Buffering on Transmit: Double Buffering on Receive: 6% d) In an SPI transfer between two MC68HC11’s with CPHA = 1 and POL = 0, a fixed Master is attached to only one slave. Draw the required connections between the machines and/or tie lines to appropriate voltage levels. Use Word 6.0c or later to view Macintosh picture. 3% e) A student wrote a correct program segment to clear RTIF in TFLG2. The student ran the program on SIM11 and then examined the TFLG2 register after terminating the program and discovered that RTIF was not cleared! Explain what caused this behavior.
25% 5. A psychologist places a lever in a chimpanzee’s cage and seeks to measure how fast the
chimpanzee looses interest in pressing the lever to obtain a banana reward. To condition the chimp, each of the first 4 lever presses releases a banana piece into the cage. Thereafter, the number of lever presses required to release a banana piece increases by a factor of two after each successive group of 4 presses. Hence, after four successes at 1 press/reward, the system
DEPT. ECE, EEL 4744 C FINAL EXAM Antonio A. Arroyo, Keith L. Doty NAME_________________________________________________________ SS#_________________________________________________________
