Objective

The purpose of this assignment is to illustrate how the $.$FILL pseudo$-$op performs the task of translating textual decimal numbers $($such as the string $+5392)$ into actual numbers $($i$.$e$.$ five thousand three hundred and ninety two, represented of course as a $16-$bit two's complement binary value$).$

High Level Description

Prompt the user to enter a signed multi$-$digit decimal number $($max $5$ digits$)$ from the keyboard. Convert the string of decimal numeric digits into the corresponding $16-$bit two's complement number, stored in Rx $($i$.$e$.$ one of the $8$ registers: you will be told which register at the start of the provided starter code$).$

The range of acceptable values is $[-32768,+32767]$; the absence of a sign means the number is positive $-$ i$.$e$.$ the first character entered by the user may be $\text{'}+\text{'},\text{'}-\text{'},$ or a numeric digit $-$ and nothing else.

Your Tasks

Your program can be broken down into the following tasks: $1.$ Read in the initial character.

$$ If it is a $-,$ make the final result negative by setting a "flag" $($so if the "negative" flag is set, take the $2$s complement of Rx at the end$).$

$$ If it is $\text{'}+\text{'}$ it can be ignored;

$$ If it is a numeric digit, then the number is not negative, and the input is just the first numeric digit of

the number.

$$ In all three cases, you can then proceed to accept any remaining digits $($see item $2.)$

$$ If the initial character is a newline, the program can just terminate without any output.

$$ Any other initial character must be treated as an error $($see below$).$

$2.$ Convert the string of numeric digits input by the user into the binary number they represent $($see examples below$).$ To do this, you can follow this algorithm:

$$ Initialize Rx $($and any other registers as needed$)$ to $0-$ DO NOT do this by LD'ing $0$ from memory! There is a much simpler & faster way $-$ remember the "TIP" in your lab $1$ notes!

$$ Convert each digit from ascii code to binary number as it is typed in$,$ and add it to Rx;

as each subsequent digit is entered, multiply Rx by #$10,$ and repeat

$($go back to lab $1$ & assn $1$ to recall how to multiply!$)$

Stop when you detect the newline character $(\text{'}$

$\text{'}=$ x$0$A$),$ or when you reach $5$ input digits:

$$ For example, if the user types $2,$ then Rx will contain #$2=$ b$0000000000000010$

$$ If the user then types $3,$ making the string now read $23,$ then Rx will contain $2$ x #$10+3=$ #$23=$ b$0000000000010111$

$$ If the user then types $4,$ making the string read $234,$ then Rx will contain #$23$ x #$10+4=$ #$234=$ b$0000000011101010$

You must also perform input character validation with this assignment $$ i$.$e$.$ reject any non$-$numeric input character. That is$,$ if the user enters $+23$g$,$ on detecting the non$-$numeric $\text{'}$g$\text{'},$ your program should output an error, discard all input, and start over with the initial prompt $($see sample output$).$

You must also count the number of characters entered $-$ once it gets to $5$ you should stop accepting new characters, and issue a newline $($in this case, do not wait for the user to hit Enter$).$

However, you do not have to detect overflow in this assignment $$ we will only test your code with inputs in the range $[-32768,+32767].$

Expected $/$ Sample output

Output

$$ Prompt

$$ "Input a positive or negative decimal number $($max $5$ digits$),$ followed by ENTER

$"$

$$ Error Message

$$ "ERROR! invalid input

$"$

Example

If the user enters $+7246,$ your program should read the $+,7,2,4,6$ and end up with the value b$0001110001001110($which is the two's complement representation of the number #$7246,$ or x$1$C$4$E$)$ in the specified register.

If the users enters $-14237,$ your program should read the $-,1,4,2,3,7$ and end up with the value #$-14237=$ xC$863=$ b$1100100001100011$ in the specified register.

WARNING: In the following examples, the final result is shown in R$5,$ which may NOT be the one you will use. You will store your result in the register specified in the header in your starter code!!

Make sure you get this right, or the grader will not work, and you will get $0/10!$