CS 273

Homework 3 Solution

Show all your work. If you do not show your work, you get no credit.

From the Book

from page 109-110

• 2-4 (8 points)

  Figure 2-26, with N,Z,V,C condition code bits.

  Assembly	Address	Contents
  N1	0010	02

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  Assembly	Address	Contents	N	Z	V	C
  LDAA	c200	B6
  EXT	c201	c3
  	c202	45	0	0	0	-
  LDAB	c203	d6
  DIR	c204	10	0	0	0	-
  ABA	c205	1b	0	0	0	0
  STAA	c206	b7
  EXT	c207	c3
  	c208	46	0	0	0	-
  STOP	c209	3f	-	-	-	-

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  Assembly	Address	Contents
  N2	c345	29
  SUM	c346	ff



• 2-19 (2 points)
  

  C bit: For unsigned binary numbers has meaning because indicates that not enough bits were available to represent the unsigned value (need to extend bits); for 2C binary numbers has no meaning because may be the artifact of adding two negative signed numbers.

  V bit: For unsigned binary number has no meaning because there is no sign bit so can not add two positives and get a negative or visa versa; for 2C binary numbers has meaning because there is a sign bit (MSB) and may add two positives and get a negative or visa versa.

from page 143-144

• 3-5 (10 points)

  0001						**	Assembler		Exercise
  0002						**
  0003	000c(a)					model		equ		12
  0004	0030							org		$0030
  0005	0030					temp(b)		rmb		1
  0006	d300							org		$d300(c)
  0007	d300	0c				type		fcb		model
  0008	d301	01	03(d)			size		fdb		$0103
  0009	d303
  0010	c000							org		$c000
  0011	c000	ce	d3	01(e)		start		ldx		#size
  0012	c003	f6	d3	00(f)				ldab		type
  0013	c006	17(g)						tba
  0014	c007	97	30					staa		temp(h)
  0015	c009	27	05			again		beq		next(i)
  0016	c00b	5c						incb
  0017	c00c	6a	01(j)					dec		1,x
  0018	c00e	20	d3(k)					bra		again
  0019	c010	d7	30			next		stab		temp
  0020	c012	3f				last		swi
  0021								end
  Defined(Line Number)					Symbol Name			Value		Reference
  *0015					again(l)			c009(m)		0018
  *0020					last			c012(n)
  *0003(o)					model			000c		0007
  *0019					next			c010		0015
  *0008					size			d301		0011(p)
  *0011					start			c000
  *0005					temp			0030		0014	0019
  *0007					type(q)			d300(r)		0012

• 3-6 (10 points)
  (a) The number that was stored in memory location 0030 is $0f.
  (b) The last time the BEQ instruction was executed, it (did, did not) did branch.
  (c) The number in memory location 0104 is Unknown.
  (d) The number in the X index register is $D301.
  (e) The number in the A accumulator is $0c.
  (f) The number in the B accumulator is $0f.
  (g) Would the binary code for the BEQ instruction change if the statement on line 10 were changed to ORG $DD00? NO - a BEQ instruction has relative addressing; `next' would still be 05 byte change for the PC on the branch.
  (h) List the line numbers of all the instructions that would have change binary codes if the statement on line 4 were changed to ORG $D000.
  Lines - 0014, 0019.

Not From The Book

Assembly of program (30 points)

Address	Contents		Assembly
				org	$0030
0030			temp	rmb	1

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Disassembly of program (20 points)

Address	Contents		Assembly
				org	$0012
0012			workstor	rmb	1

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Last modified: Mon Oct 8 23:13:49 MST 2001