Low Level Breakdown

This assignment comprises five tasks:

$1.$ Prompt the user, and read two numeric characters $(\text{'}0\text{'}...\text{'}9\text{'})$ from the user using Trap x$20$

$($GETC$).$ Echo the characters to the console as they are received $($OUT$),$ and store them as

character data in separate registers.

$2.$ Output to the console the operation being performed e$.$g$.$

$5-7=$

$($how will you print the $"-"?$ How will you print the $"="?$ Note the double quotes!!$)$

$3.$ Once the setup is printed, convert the numeric characters into the actual numbers they

represent $($e$.$g$.$ convert the ASCII code for $7$ into the binary representation of the number $7).$

$4.$ Perform the subtraction operation $($by taking the two's complement of the second operand and

adding$),$ and determine the sign $(+/-)$ of the result;

if it is negative, determine the magnitude of the result $($i$.$e$.$ take the $2\text{'}$s complement to turn it

back into a positive number$).$

$5.$ Convert the resulting number back to a printable character and output it$,$ together with a minus

sign if necessary. Remember, the number $-4$ when converted to text is actually two separate

ascii characters, $\text{'}-\text{'}$ and $\text{'}4\text{'}.$

Example, with a detailed algorithm $($we won't always give you this!$)$

$$ Program prompts for user input $($two characters$)$:

$$ user enters $5,$ which is echoed to console $($followed by a newline$)$ and copied to a register.

$$ user enters $7,$ which is echoed to console $($followed by a newline$)$ and copied to a different

register.

$$ Program outputs the text

$5-7=$

$($this will actually require at least $4$ distinct output steps using OUT and PUTS$)$

$$ Program converts $5($ascii code$)$ into $5($number$)$ and stores it back in the same register.

$$ Program converts $7$ into $7$ and stores it back in the same register.

$$ Program takes $2\text{'}$s complement of $7,$ and stores the result back into the same register.

$$ Program adds the contents of the two registers $-$ i$.$e$.$ it performs the operation $(5-7)$ and stores

the result $(-2)$ in a third register.

$$ Program recognizes that the result is negative, obtains the magnitude of $-2(=2),$ and outputs $\text{'}-\text{'}$

$($minus sign$).$

$$ Program converts $2($number$)$ into $\text{'}2\text{'}($ascii code$),$ and stores it back in the same register.

$$ Program outputs $\text{'}2\text{'}$ followed by a newline.

Expected$/$ Sample output

In this assignment, your output must exactly match the following, including:

$$ the prompt, followed by newline $($provided in the starter code$)$

$$ Each digit input "echoed" and followed by a newline

$$ the subtraction operation, including spaces as shown, also followed by a newline:

$($Difference is Positive$)$

$($Difference is Zero$)$

$($Difference is Negative$)$

Your code will obviously be tested with a range of different operands giving all possible results.

Make sure you test your code likewise!

NOTES:

$$ All console output must be NEWLINE terminated.

$$ We will test only with positive single digit numeric inputs

$$ NO error message is needed for invalid input $($i$.$e$.$ we will not test with non$-$numeric inputs$)$Console $($click to focus$)$

$\stackrel{}{x}$

$($Difference is Positive$)$

Console $($click to focus$)$

x

ENTER two numbers $(1.$e $\text{'}0\text{'},..\text{'}9\text{'})6$

$6$

$6-6=0$

$---$ Halting the LC$-3--$I

$($Difference is Zero$)$

Console $($click to focus$)$

ENTER two numbers $($i$,$e ${10}^{\text{'}}$dots.${\mathrm{.}9}^{\text{'}})$

$2$

$7$

$2-7--5$

$---$ Halting the LC$-3$