CSCI 2150
Fall 2000 Final Exam -- Answers

The following is the answer key to the Fall 2000 CSCI 2150 Final Exam. In some cases, where the HTML does not prohibit it, I've elaborated on the process to get to the answers.

1. If the zero flag (ZF) is set to one, what will the processor do if it encounters the instruction JG  LABEL?
   
   Answer: B
   
   
2. If IP=1435 hex and CS=0407 hex, what is the physical address of the next instruction to execute?
   
   Answer: Answer: Begin by shifting the segment register CS 4 bit positions to the left and "back-filling" with zeros. This gives us 04070₁₆. Then add the result of this operation to the pointer register IP. This gives us:
   
   04070₁₆ + 1435₁₆ = 054A5₁₆
   
   
3. If a processor takes 3 cycles to execute any instruction (fetch, decode, execute), then how many cycles would it take to execute 5 instructions if the processor is pipelined?
   
   Answer:
   
   piplined = 2 initial cycles + 1 cycles/instruction * 5 instructions
   piplined = 7 cycles
   
   
   
   
4. For each of the following assembly language instructions, identify which registers and flags are affected and enter the updated value if you have enough information. (Just put an 'X' in the box if it's impossible to know the new value.) Use the memory contents shown in the chart below if necessary. For each instruction, assume all registers contain 0 before execution.
   
   Answer:
   

5. Name the two reasons covered in class for using segmented addressing in the 80x86.
   
   Answer:
   
   
   • Allows for relocatable code
   • Allows processor to access 20 address lines using only 16-bit registers
   
   
   
6. Of the following registers, which are 8 bit registers?
   
   Answer: BH and CL
   
   
7. Indicate whether the following statements are true or false.
   
   Answer:
   
   F -- The assembly language instruction CMP does not alter any processor flags
   T -- To read from an I/O port, the ^IORC line is pulsed low.
   T -- All Intel 80x86 and Pentium processors can address no more than 64K ports
   F -- The newer bi-directional parallel ports have 16 data lines
   F -- The 5 input and 5 output control lines of the parallel port cannot be used for general-purpose applications, i.e., non-printer applications.
   F -- The printer port on a PC is interfaced to the processor with memory mapping.
   T -- USB allows users to plug and unplug equipment without rebooting.
   F -- A null modem is used to connect a DCE device to a DCE device.
   
   
   
8. Draw the entire signal that is produced when a serial interface transmits the character ';' with eight-bit data, one stop bit, and odd parity. (ASCII ';' = 3Bh) In addition, identify each part of the signal.
   
   Answer:
   
   
   
   
9. If it takes 2.5 microseconds (1 microsecond = 10^-6 seconds) to transmit one bit across a serial interface, what is the baud rate?
   
   Answer:
   
   BAUD rate = 1/bit time
   BAUD rate = 1/2.5x10^-6
   BAUD rate = 400,000 bits per second
   
   
10. If the baud rate is 9600 bits per second across a link with 1 stop bit, even parity, and 7 data bits, how many data bits per second are being transmitted?
    
    Answer:
    
    data bits per second = BAUD rate * (# of data bits/# of frame bits)
    data bits per second = 9600 * (7 data bits/(7 data bits + 1 start bit + 1 stop bit + 1 parity bit))
    data bits per second = 9600 * (7 data bits/10 frame bits)
    data bits per second = 6720 bits per second
    
    
11. Classify each of the following characteristics as RS232 serial (R), USB (U), GPIB (G), or SCSI (S).
    
    Answer:
    
    U -- Two speeds -- 1.5 Mbps and 12 Mbps
    R -- Serial point-to-point communications
    U -- Can have up to 127 active devices on a single connection
    G -- Can have at most 15 active devices on a single connection
    U -- Contains power supply lines in a four conductor connection
    R -- Uses voltage levels of -12 volts for a logic 1 and +12 volts for a logic 0
    R -- Requires only three conductors for a minimum connection
    S -- Primary applications include disk drives, tape drives, and CD drives.
    
    
    
    
    
12. Assuming V_rl=0.5 Volts and V_rh=4.0 Volts, produce the table of samples output by a three-bit ADC starting at t=0 milliseconds with a sample taken every 5 milliseconds (1 millisecond = 10^-3 seconds).
    
    Answer:
    
    

13. What would the accuracy (to 4 decimal places) of this system be if we used a 10 bit ADC?
    
    Answer:
    
    accuracy = range/(number of increments)
    accuracy = (4.0V - 0.5V)/(2¹⁰ - 1)
    accuracy = 3.5V/1023
    accuracy = 0.003421
    
    
14. What is the highest frequency we could measure with this system?
    
    Answer: The highest frequency measureable with this system is half the sampling rate. Since the sampling rate = 1/(time between samples) = 1/5 milliseconds = 200 Hz, then the highest frequency we can capture = 200 Hz/2 = 100 Hz.
    
    
15. What do the following analog sensors read and what type of output do they have?
    
    Answer:
    
    

16. What is the purpose of a Wheatstone bridge?
    
    Answer: To convert very small changes in resistance to measureable changes in voltage.
    
    

Created by David Tarnoff for use by his sections of CSCI 2150.