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CS $2810$

Programming Assignment $2$

Hello World!

Objective:

The objective of this lab assignment is to demonstrate your ability in

Using TRAP routines to get input from keyboard and output to the console

Detecting the end of user input with a newline character $($x$0$A$)$

Lab Statement:

You will write a program in LC$-3$ machine code that will do the followings:

$1.$ Detect a user input from the keyboard and echo the input to the console

$2.$ Store the user input beginning at $0$x$3011.$ The first character will be stored in location

$0$x$3011.$ The second character will be stored in location $0$x$3012,$ etc.

$3.$ The user input will end with a return key which will be interpreted by LC$-3$ as a newline

character $(0$x$0$A$)$

$4.$ Upon detecting a newline character, display the entire user input to the console.

$5.$ Terminate the program.

LC$-3$ Syntax:

$1.$ Get a character from keyboard.

LC$-3$ has a TRAP service routine, trap vector x$20,$ that will get a character from the

keyboard. It will store the character in register R$0.$

Opcode: $1111$

Operand $1$: x$20($trapvect$8)$

Note: This instruction moves the user input to R$0$ directly without echoing the

user input to the console. If you want to see the user input, you need to

display it through your code, see next bullet item.

Instruction: $1111000000100000=$xF$020$

$2.$ Echo a user input to the console

LC$-3$ has a TRAP service routine, trap vector x$21,$ that will put the character in R$0$ to the

console. If you call this service routine right after you get a user input, the user input will

be echoed to the console.

Opcode: $1111$

Operand $1$: x$21($trapvect$8)$

Note: This instruction displays the content in R$0$ to the console if it is a printable

ASCII character.

Instruction: $1111000000100001=$xF$021$

$3.$ Detecting a Newline Character

The ASCII code of the newline character is x$0$A$.$ To detect a newline character, you need

to compare the user input with x$0$A$.$ One of the ways to do this is to add the user input

with the $2$s complement of x$0$A$,$ ASCII code of newline character. If the result is $0,$ then

the user entered a newline character.

$4.$ Move the input to memory

One of the ways to move the user input to the memory is using an STR instruction. STR

requires a source register whose content is the data that needs to be stored, a register

to store the base address, and a six$-$bit offset. In our case, the register that contains the

data is R$0.$ You can choose a register to store the base address. One suggestion is to

store x$3011$ in that register. For the first character, we will use an offset of $0.$ For the

additional character, instead of increasing the offset, it is easier to increment the base

address in the register.

Opcode: $0111($STR$)$

Operand $1$: $000($SR$)$

Operand $2$: register of your choice. $($BaseR$)$

Operand $3$: required offset based on your design

Instruction: If I use R$5$ as BaseR and $0$ for the offset, the instruction will be

$0111000101000000($or x$7140)$

$5.$ Stay in the loop

You can use the BR $(0000)$ opcode to stay in a loop that reads the input from keyboard

until the newline character is detected.

$6.$ Display a string

LC$-3$ has a trap service routine, trap vector x$22,$ that displays a null$-$terminated string to

the console. To utilize this routine, you need to put the beginning address of the string

into R$0$ before you call this routine. In our case, the beginning address of the user input

is x$3011.$ Make sure you add a null character at the end of string when you detect a

newline character.

Testing:

Enter $$Hello LC$-3,$ this is $.$ from the keyboard. For example, if I am

testing the program that I write, I will enter $$Hello LC$-3,$ this is ACT.$$

Note: It is too complicated to implement the backspace key at this point. Make sure you

enter the correct string.

Submission:

$1.$ Your machine code, either in binary or hex, in a text file.

$2.$ A screenshot shows your interaction with LC$-3,$ see sample screenshot below.

please remember to write in machine code, as well to make sure this works for the LC$-3$ machine code simulator thank you.