University of Florida EEL 4744 Spring 2014 Dr. Eric M. Schwartz Department of Electrical & Computer Engineering 1 April Apr-14 9:03 AM

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You may use any of your XMEGA documents with limited added material; highlighting and tagging is permissible.

1 Page 1/15 Exam 2 Instructions: Turn off cell phones beepers and other noise making devices. BEAT UCONN! Show all work on the front of the test papers. If you need more room make a clearly indicated note on the front of the page "MORE ON BACK" and use the back. The back of the page will not be graded without an indication on the front. You may use any of your XMEGA documents with limited added material; highlighting and tagging is permissible. You may not use any notes (mine or yours) examples homework labs books calculators computer electronic devices etc. Put your name at the top of each test page and be sure your exam consists of 15 distinct pages. The space provided does not necessarily represent the amount of writing necessary. You must pledge and sign this page in order for a grade to be assigned. May the Schwartz In programs the use of comments results in more partial credit. Read each question carefully and follow the instructions. be with you! The point values for problems may be changed at prof s discretion. Part of your grade on tests quizzes labs etc. is based not only on solving the problem you are presented with but the manner in which you solve it. For example there is a difference between two programs that meet the given specifications but one is an elegant extensible 20-line solution while the other is an obfuscated 100-line program that also meets the specifications but would be difficult to extend later. Just as your future employer would value the latter program less than the first so will I in grading your assignments. This exam counts for % of your total grade. Unless otherwise stated assume the following: Go Good * The oscillator frequency is precisely 2 MHz. * The code should run on an ATxmega128A1U as configure on the UF utinkerer Development Board without any additional peripherals. Gators! luck! * PLEDGE: On my honor as a University of Florida student I certify that I have neither given nor received any aid on this examination nor I have seen anyone else do so. PRINT YOUR NAME SIGN YOUR NAME DATE (1 April 14) Regrade comments below. Give page # & problem # and reason for the petition. Pages Available Points TOTAL 100

2 Page 2/15 Exam 2 [11%] 1. An analog to digital converter (ADC) system uses 6 bits unsigned and has an analog input range from 2.7V to 9.7V (VRefL and VRefH respectively). Show all work in each of the problems below. (4%) a) Derive a formula to determine the analog voltage (v in decimal) from the 6-bit unsigned digital ADC value (ADC in decimal) v = f( ADC ). 4 min v = (1%) b) What is the voltage (in decimal) if the ADC returns a binary value of ADC = ? 1 min (2%) c) If v = 4.7V is a valid input what is the captured ADC value (in decimal and binary)? If the value is not valid write not valid? v = (1%) e) What is the resolution for this ADC system? 1 min ADC = = (3%) e) With your utinkerer board's internal clock set at 2 MHz how many clock cycles are available to perform a single analog to digital conversion if an external interrupt has a frequency of 20 khz? # clock cycles =

3 Page 3/15 Exam 2 [2%] 2. The XMEGA s ADC is initialized to read in a value at PORTA using the ADC s channel 2. In assembly (NOT mixed assembly) set up the corresponding interrupt vector so that the interrupt service routine ADC_ISR is executed when the ADC conversion is complete. Labels Instructions Comments [9%] 3. The XMEGA s asynchronous serial communications will be used in this problem. (4%) a) Draw the timing diagram for a serial communication frame if it consists of one (1) start bit seven (7) data bits (with data 0x37) no parity and two (2) stop bits. Label the bits. 4 min (1%) b) If even parity is set for the above serial communication what is the value in the parity bit? Why? 1 min Parity = (1%) c) If odd parity is set for the above serial communication what is the value in the parity bit? Why? 1 min Parity = (3%) d) If NO parity is used for the above serial communication how long does it take to transmit 1000 ASCII characters (of 7 bit data) when the baud rate is 50 khz? Time =

4 Page 4/15 Exam 2 [18%] 4. You are working on a team project that requires an audio circuit. Other students on your team have wired up an analog signal from an amplified and filtered microphone to the ADC on 4 min your board (more specifically AD 3). Your job is to read an input connected to an interrupt pin (port D pin 4) to turn ON and OFF the ADC conversions. The storage of the ADC values is NOT part of your required design but you should assume that when the ADC is on the data is coming in continuously and will be stored as each new value is received. 7 min You will write three subroutines in MIXED C / ASSEMBLY. You will write an INIT_ISR subroutine (in C) that will initialize the interrupt service routine for the external interrupt. You will also write an INIT_ADC subroutine (in C) that will initialize the ADC. You are also required to write an interrupt service routine (in ASSEMBLY) for the interrupt that will turn OFF the ADC conversion if it is on and will turn it ON if the ADC conversion is off. The only requirement for the ISR is that it should be a low level interrupt and be triggered on both edges. (A more sophisticated solution would be to use the two edges separately but that is not necessary or desired in this problem.) The ADC should be configured with an internal reference of Vcc / 1.6 and should be unsigned with a resolution of 12 bits. Assume all files that need to be included are and that a main function is already written. Do not forget to push registers if appropriate (especially in the ISR). Be sure to write function prototypes if needed. Be sure to comment your code if you want to maximize your partial credit. (8%) a) Write the initializations and required protoypes in C for the ISR and the ADC. C Code Comments

5 Page 5/15 Exam 2 3 a) (continued) C Code Comments (10%) b) Write the ASSEMBLY subroutine for the ISR. Don t forget to name your subroutine appropriately (remember that this is MIXED C). 10 min Labels Instructions Comments

6 Page 6/15 Exam 2 3 b) (continued) Labels Instructions Comments

7 Page 7/15 Exam 2 [33%] 4. In this problem you will write parts of a program to interface a wireless radio using your utinkerer board to your LCD screen. This wireless radio communicates with your 4 min microprocessor much like the USB-to-serial converter IC used on your utinkerer board. The transmitter on the other side of the radio link sends messages composed of 16 ASCII characters but it does so very slowly (compared to the speed of the LCD) so you should only update the LCD screen after the entire message has been received. All messages that your radio receives will be exactly 16 characters long (which is coincidentally the same number of characters that fit on one line of your LCD). Your LCD should always display the latest complete message that you have received from the radio. The wireless radio is connected to USARTE0 on your XMEGA and sends serial data to the XMEGA with the following characteristics: 7 bit data 1 stop bit odd parity and a baud rate of 20 khz. (You must use BSCALE = -3.) You do not need to send any data to the wireless radio (it is a receive-only radio link). (2%) a) How will you configure the 20 khz baud rate? Calculate specific value(s) that you will need later. You must use BSCALE = -3. The LCD's command register is at 0x The necessary decoding equation has already been created for you in the CPLD but you must configure CS3 using the smallest chip-select size and select a base address that is appropriate. The LCD's RS pin is connected to address pin A0 as it was in your Lab 6. (4%) b) What is the base address and address size that you will use for the above LCD. Show 5 min your work. What changes if any must be made to the utinkerer in order to properly generate the address decoding requested above? You may assume that the following LCD functions have been written for you: LCD_INIT(): performs all necessary LCD initialization commands LCD_CLEAR(): clears the screen and returns home LCD_POLL(): returns only when the LCD is ready for new data i.e. not busy Your microprocessor is also being used to perform other important work (not pertaining to USARTE0 or the LCD screen) so you should use an ISR to receive message from the radio. You should generally not update the LCD screen in your receiver ISR but it is acceptable to do so if you find it easier. You must configure your receive interrupt as low-level priority.

8 Page 8/15 Exam 2 4. (continued) For this program you must write code completely in C. The ebi_driver.h file from our website is available for your use. For all configuration values write out the values in binary or hex. Do NOT use the group configuration (_gc) or bitmask (_bm) constants. Below you will write the following C code: main() USART_INIT() EBI_INIT LCD_OUT_CHAR and the ISR for USARTE0. (0%) 4. c) Draw a flowchart or write pseudo-code to describe the behavior of the main() function as 7 min well as the receiver ISR.

9 Page 9/15 Exam 2 (5%) 4. d) Write the USART_INIT() function. Make sure to initialize all the necessary functionality to enable the receive interrupt with low-level priority. 4 min C Code Comments (7%) 4. e) Write the EBI_INIT() function to enable CS3 for the LCD at 0x as described. 4 min C Code Comments

10 Page 10/15 Exam 2 (3%) 4. f) Write the LCD_OUT_CHAR() function. C Code Comments (6%) 4. g) Write the receive ISR for USARTE0. 6 min C Code Comments

11 Page 11/15 Exam 2 (6%) 4. h) Write the main() function. Be sure to call any necessary initialization functions (i.e. those that were provided and those that you have written above). 6 min C Code Comments

12 Page 12/15 Exam 2 [18%] 5. Answer each of these short questions. (2%) a) When calculating baud rates for your processor it is important that the values of BSEL and BSCALE be calculated and chosen correctly to reduce timing error. Briefly explain why this error exists and how it affects the communication between the two devices. (2%) b) Your XMEGA chip has many dedicated USART hardware peripherals for interacting with external serial devices. If you need even more USARTs than are available how (if possible) could you still add transmit to a serial device? (2%) c) Your XMEGA chip has two dedicated USART hardware peripherals on each port for which USART is available. Is it possible to use both at once and also receive external interrupts on other pins in the port? Why or why not?

13 Page 13/15 Exam 2 (2%) 5. d) In the LCD setup you implemented you tied A0 to the Data/Command line of the LCD. Could you use a non-address pin for this function? If so describe how and what you would do. (2%) e) In the initialization of the EBI for correct functionality there are certain ports (e.g. Port A or Port B) that require setup. Which signals associated with the EBI REQUIRE that you make direction assignments? Why? (2%) f) In addition to these ports that have specific requirements for their direction (see above question) there are default values that must be written to certain pins. What are these values and on which pins are required? Why are these necessary?

14 Page 14/15 Exam 2 (2%) 5. f) If two interrupts have the same priority level and both occur at the same time which one will be executed/interrupted first? (2%) f) What is the most likely cause of the error when an RTC timer is setup to interrupt every 37 seconds but after the first interrupt occurs a second interrupt happens almost immediately? (2%) g) In the XMEGA s ADC when using signed mode the negative reference voltage is just the negative of the high reference voltage. This is not the case in some processors and some external ADC chips where the two references are independent. If the negative reference is -3V and the positive reference is 7V what is the voltage for an 8-bit ADC output of 0x ? Show your work.

15 Page 15/15 Exam 2 [9%] 6. In this problem you will design an expansion to a utinkerer board by adding a memorymapped 8-bit LCD (as described in problem 4) an external interrupt (port D pin 4 as 10 min described in problem 3) from an active-low SPST switch a potentiometer output (between 0 and 1V) to an ADC (AD 3 as described in problem 3) a serial receiver (on USARTE0) from a wireless radio (as described in problem 4) and a CPLD (as described in problem 4). Show only the necessary pins and connections.

University of Florida EEL 3744 Spring 2017 Dr. Eric M. Schwartz Department of Electrical & Computer Engineering 22 February Mar-17 1:44 PM

University of Florida EEL 3744 Spring 2017 Dr. Eric M. Schwartz Department of Electrical & Computer Engineering 22 February Mar-17 1:44 PM Page 1/11 Exam 1 Instructions: Turn off cell phones beepers and other noise making devices. Show all work on the front of the test papers. If you need more room make a clearly indicated note on the front