EE345M Final Exam Spring 2009 Page 1 of 8 Jonathan W. Valvano First Name: _______________ Last Name:____________________ May 14, 2009, 2-5pm Open book, open notes, calculator (no laptops, phones, devices with screens larger than a TI-89 calculator, devices with wireless communication). Please don’t turn in any extra sheets. (6) Question 1. Consider how the ACK bit is used in a CAN network. Part a) What do the receivers do during the ACK bit? Part b) What does it mean if the ACK bit is high? Part c) What does it mean if the ACK bit is low? (4) Question 2. When designing a low power system, give the equation that defines power budget. Explain (define) each of the terms in the equation.EE345M Final Exam Spring 2009 Page 2 of 8 (15) Question 3. Consider the following motor interface. A series-wound DC motor, like the ones in the robot kit, can be modeled by a series combination of a resistor (the ohmic contribution of the long thin wires used to wrap the electromagnets), an inductor (physically resulting from the cylindrical manner in which the electromagnets are wound), and an emf (a voltage caused by the load torque applied from the shaft back into the electromagnet). The resistance is what you get when you measure the resistance of the motor with an ohmmeter (a stopped motor, disconnected from power). In this motor, R = 100 Ω and L = 100 μH. Hint: L/R is 1 μsec. Part a) Under maximum load, VCE is 0.75V, the emf becomes –12.35V, and 0.2A flows through the motor. What transistor do you choose for this interface (specify part number)? Why? Part b) What value do you choose for Rb? Show your work using the labels from the picture. Part c) Initially the motor is on (0.2A current to the motor). At time t=0, the digital port goes from +5 to 0 and transistor turns off. At time t=0-, the emf is –12.35V (motor has external torque applied to the shaft) and the transistor turns off instantaneously. First, assuming there is no 1N914, graph the collector voltage (VCE) as a function of time. Second, graph VCE with the 1N914. ICVCE+-+-VBER9S12-+VOHPortIBMotor+8.4V-+RLemf-+b1N914EE345M Final Exam Spring 2009 Page 3 of 8 (10) Question 4. Design a two-pole analog low-pass filter with a cutoff frequency of 10 Hz. Show the design steps, and specify resistor/capacitor values, choosing standard values. Standard values for 5% resistors range from 10 Ω to 22 MΩ. We can multiply a number in Table 1 by powers of 10 to select a standard value 5% resistor. For example, if we need a 25 kΩ 5% resistor, the closest number is 24*1000, or 24 kΩ. Table 2 shows standard capacitor values. 10 11 12 13 15 16 18 20 22 24 27 30 33 36 39 43 47 51 56 62 68 75 82 91 Table 1. Standard resistor values for 5% tolerance 10pF 100pF 1000pF 0.010μF0.10μF 1.0μF 10μF 12pF 120pF 1200pF 0.012μF0.12μF 1.2μF 15pF 150pF 1500pF 0.015μF0.15μF 1.5μF 18pF 180pF 1800pF 0.018μF0.18μF 1.8μF 22pF 220pF 2200pF 0.022μF0.22μF 2.2μF 22μF 27pF 270pF 2700pF 0.027μF0.27μF 2.7μF 33pF 330pF 3300pF 0.033μF0.33μF 3.3μF 33μF 39pF 390pF 3900pF 0.039μF0.39μF 3.9μF 47pF 470pF 4700pF 0.047μF0.47μF 4.7μF 47uF 56pF 560pF 5600pF 0.056μF0.56μF 5.6μF 68pF 680pF 6800pF 0.068μF0.68μF 6.8μF 82pF 820pF 8200pF 0.082μF0.82μF 8.2μF Table 2. Standard capacitor values for 10% toleranceEE345M Final Exam Spring 2009 Page 4 of 8 (25) Question 5. Consider the following implementation of OS_AddThread, similar to the one given in the Lab 17 starter file. struct TCB{ struct TCB *Next; // Link to Next TCB unsigned char *StackPt; // Stack Pointer unsigned char MoreStack[101]; // additional stack unsigned char InitialCCR; unsigned char InitialRegB; unsigned char InitialRegA; unsigned short InitialRegX; unsigned short InitialRegY; void (*InitialPC)(void); }; typedef struct TCB TCBType; typedef TCBType * TCBPtr; TCBType SystemTCB[MAX_THREADS]; unsigned short static NumThread=0; // number of threads TCBPtr RunPt; // Pointer to thread currently running //******** OS_AddThread *************** // add a foregound thread to the scheduler // Inputs: pointer to a void/void foreground function // Outputs: 1 if successful, 0 if this thread can not be added short OS_AddThread(void(*fp)(void)){ if(NumThread >= MAX_THREADS){ return 0; // structure is full } if(NumThread){ SystemTCB[NumThread-1].Next = &SystemTCB[NumThread]; } SystemTCB[NumThread].StackPt = &SystemTCB[NumThread].InitialCCR; SystemTCB[NumThread].InitialCCR = 0x40; // I bit clear SystemTCB[NumThread].InitialPC = fp; // Initial PC SystemTCB[NumThread].Next = &SystemTCB[0]; // link NumThread++; return 1; } Redesign the system so that if the user program finishes, the OS will run the user program again. For example, this user function executes stuff1, stuff2 and stuff3 once and quits. void user(void){ stuff1(); stuff2(); stuff3();} If the user calls this system function to activate user, OS_AddThread(&user); then with your updated system stuff1, stuff2 and stuff3 will be repeated over and over again. You are allowed to make changes to the struct and to OS_AddThread, but not to user or other OS functions. You can however add additional OS functions. In particular, show changes to the struct and rewrite OS_AddThread in its entirety.EE345M Final Exam Spring 2009 Page 5 of 8EE345M Final Exam Spring 2009 Page 6 of 8 (16) Question 6. List the four design choices one must make when implementing a spectrum analyzer (ADC->FFT->graphics display) like the spectrum analyzer that generated the following figure. For each of the four choices, explain what the consequences are of that choice. I did not mean circuitry in front of the ADC, such as anti-aliasing analog low pass filter, analog circuit gain, analog input impedance, 1) Design choice and what does it mean? 2) Design choice and what does it mean? 3) Design choice and what does it mean? 4) Design choice and what does it mean?EE345M Final Exam Spring 2009 Page 7 of 8 (24) Question 7. The overall goal is to design a feedback motor controller based on motor current IC. The specific goal of this question is to add functionality to the following motor control circuit to allow the microcontroller to measure IC. You may assume IC is always