Midterm Solutions Fall 2008

PwnHero October 20th, 2008 COE 538 Midterm Name: _____________________________ Student #: __________________ Time: 90 min. Notes: 1. Closed book. 2. Write the answers in the space provided. 3. The Instruction Set can be detached. 4. No question during the exam. State your assumptions. 1. Questions on Subroutines and Interrupt Service Routines: a) Which instruction should be used to exit a subroutine? [1 mark] RTS b) Which instruction should be used to exit an interrupt service routine? [1 mark] RTI c) What are the differences between these two instructions? [3 marks] RTI returns PC, X, Y, A, B, CCR RTS returns PC only. 2. What is the value stored in the general purpose accumulator D after each of the following instructions is executed? Use hexadecimal notation. [5 marks] Instruction Content of D LDD #$1AB7 $1AB7 ADDA #@57 $49B7 SUBB #23 $49A0 SUBD #$023A $4766 LDAB #%10101100 $47AC @ 57 = $2F; 23 = $17 3. Assume that the VRH and VRL inputs to the 68HC11 A/D converter are 4.5V and 0V, respectively. What is the corresponding voltage value for the conversion result of 158? [3 marks] 4.5 V – 255 ? – 158 158 x (4.5 / 255) = 2.788 V 4. Draw the top 12 bytes of the stack immediately after the PSHY instruction is executed. Also state the content of the stack pointer, the index register X and general accumulator A after the LDAA 9,Y instruction is executed. Assume the initial value of the stack pointer is $0037. [10 marks] PwnHero.com