Quiz1F04Sol - before the decrement which is $3900(15...

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EE319K Fall 2004 Quiz 1A Solution Page 1 Jonathan W. Valvano September 24, 2004 10:00am-10:50am (5) Question 1. C) drop out (5) Question 2. %11010011= -128+64+16+2+1 = -45 (4) Part 3a. 101+210 = 311, which wraps around to 311-256= 55 (2) Part 3b. To find the C bit, do the math in unsigned math, which is 101 + 210 = 311. The carry bit is 1 because 55 is the wrong answer. (2) Part 3c. To find the V bit, do the math in signed math, which is 101 + -46 = 55. The overflow bit is 0 because 55 is the correct answer. (2) Part 3d. The Z bit is 0 because the result is not zero. (2) Part 3e. The N bit is 0 because the result is between 0 and 127 (bit 7 is zero). (10) Question 4. The minimum number is –128/8 which is -16 . The maximum number is +127/8 which is 15.875 . (10) Question 5. You get the opcode, E4, from the ANDB page. You get the postbyte xb , 5E, from Table A-3. Together the machine code is $E45E . (5) Question 6. Since it is a post decrement the effective address is simply the initial value of RegY
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Unformatted text preview: before the decrement, which is $3900 . (15) Question 7. There are two read cycles to fetch the opcode and operand. There are two write cycles to push the return address. The stack pointer is decremented as data is pushed, The PC is changed to point to the subroutine. R/W Addr Data Changes R $F124 $07 opcode fetch IR=$07, PC=$F125 R $F125 $66 operand fetch, PC=$F126 W $3FFF $26 push return address, SP=$3FFF W $3FFE $F1 push return address, SP=$3FFE, PC=$F18C (40) Question 8. All the object code goes in ROM org $4000 ; ROM ***********Init************** * Set direction registers so PTT are output and PTM are input * Inputs: none * Outputs: none * Errors: none Init movb #$FF,DDRT ; PTT are outputs clr DDRM ; PTM are inputs rts ***********Look************** * Look at PTM inputs, and set PTT to $55 if PTM<$20 * Inputs: none * Outputs: none * Errors: none Look ldaa PTM ; read inputs cmpa #$20 bhs skip ; leave unchanged if PTM>=$20 movb #$55,PTT skip rts...
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