All programming exercises in this homework need to be done in machine language,

not assembly language. Follow the examples in the book and add pseudocode to the

right of each instruction.

All of your programs should end with a Halt instruction:

$1111000000100101$ TRAP x$25$

$1.$ Write a short LC$-3$ program that compares the two numbers in R$1$ and R$2$ and puts

the value $0$ in R$0$ if R$1=$ R$2,1$ in R$0$ if R$1>$ R$2$ and $-1$ in R$0$ if R$1<$ R$2.$

$2.$ Section $6\mathrm{.}1\mathrm{.}4$ of the text includes an example of character counting. Why is it

necessary to initialize R$2$ in this example? In other words, in what manner might the

program behave incorrectly if the R$20$ step were removed from the code?

$3.$ Consider the following machine language program:

$0$x$30000101010010100000$

$0$x$30010001001001111111$

$0$x$30020001001001111111$

$0$x$30030001001001111111$

$0$x$30040000100000000010$

$0$x$30050001010010100001$

$0$x$30060000111111111010$

$0$x$30071111000000100101$

What are the possible initial values of R$1$ that cause the final value in R$2$ to be $3?$

$4.$ Shown below are the contents of memory and registers before and after the LC$-3$

instruction at location $0$x$3010$ is executed.

Your job: Identify the instruction stored in

$0$x$3010($all $16$ bits, not just the opcode$).$ Note: There is enough information below to

uniquely specify the instruction at $0$x$3010.$

Before After

R$00$x$32080$x$3208$

R$10$x$2$D$7$C $0$x$2$D$7$C

R$20$xE$3730$xE$373$

R$30$x$20530$x$2053$

R$40$x$33$FF $0$x$33$FF

R$50$x$3$F$1$F $0$x$3$F$1$F

R$60$xF$4$A$20$xF$4$A$2$

R$70$x$52200$x$5220$

Before After

$...$

$0$x$34000$x$30010$x$3001$

$0$x$34010$x$7$A$000$x$7$A$00$

$0$x$34020$x$7$A$2$B $0$x$7$A$2$B

$0$x$34030$xA$7000$xA$700$

$0$x$34040$xF$0110$xF$011$

$0$x$34050$x$20030$x$2003$

$0$x$34060$x$31$BA $0$xE$373$

$0$x$34070$xC$1000$xC$100$

$0$x$34080$xEFEF $0$xEFEF

$...$

$5.$ Using iteration write a program that displays the first character of your name $100$

times on the screen.

Here's the instruction to write a character to the monitor. The TRAP instruction to

write a character to the monitor assumes the character is in bits $[7$:$0]$ of R$0.$

$1111000000100001$ TRAP x$21$

$6.$ Write a program that determines if the number stored in R$4$ is odd. If the value of

R$4$ is odd, the program puts a $1$ in R$0.$ Otherwise it puts a $0$ in R$0.$

$7.$ Write a program that determines if the number stored in R$4$ is even. If the value of

R$4$ is even, the program puts a $1$ in R$0.$ Otherwise it puts a $0$ in R$0.$