LC-3 Code:

Objective

The purpose of this assignment is to illustrate how the .FILL pseudo-op performs the task of translating textual 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 in a signed multi-digit number (max 5 digits) from the keyboard. Convert the string of characters entered (as separate ascii codes for decimal numeric digits) into the 16-bit number they represent, and store the result in R5 . The range of acceptable values is [-32768, +32767]; the absence of a sign means the number is positive.

Your Tasks

Your program can be broken down into the following tasks: Read in the + or -. If the character is a -, remember to make the final result negative (i.e. take

the 2s co mplement of R5 at the end). If the result is positive then ... dont. Convert the string of characters input by the user into the binary number they represent (see

examples). To do this, you can follow this algorithm:

Initiali ze R5 to 0 (DO NOT do this by LD'ing a 0 from memory! There is a much simpler & faster way!)

Convert each digit to binary as it is typed in, and add it to R5 ; if another digit is entered, multiply R5 by 10, and repeat. Stop when you detect the ENTER (x0A):

For example, if the user types 2, then R5 will contain #2 == b0000 0000 0000 0010

If the user then types a 3, making the string now read 23, then R5 will contain 2 x 10 + 3 == #23 == b0000 0000 0001 0111

If the user then types 4, making the string read 234, then R5 will contain 23 x 10 + 4 == #234 == b0000 0000 1110 1010

You must also perform input character validation with this assignment i.e. reject any non-numeric input character.

That is, if the user enters +23g, your program should "choke" on the g, print an error message (see sample output), and start over at the beginning with the initial prompt.

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

Newline terminated Error Message

ERROR INVALID INPUT Newline terminated

Example

If the user enters +7246, your program should read the +, 7, 2, 4, 6 and end up with the value b0001 1100 0100 1110 in R5 (which corresponds to the number #7246, or x1C4E).

If the users enters -14237, your program should read the -, 1, 4, 2, 3, 7 and end up with the value #-14237 == xC863 == b11001000 01100011 in R5 .

NOTE: In the following examples, the final result is shown in R2. This is NOT the register you will be using in your code - use the register specified above!!

Note:

You must echo the digits as they are input (no "ghost writing").

You do not have to output the converted binary number. It should simply be sitting happily in

R5 , where you can check it in simpl.

What should happen when an error occurs?

Output "ERROR INVALID INPUT" and start over, prompting the user for input

Other Errors (output "ERROR INVALID INPUT" and start over):

Nothing entered before ENTER

only sign is entered before ENTER

first character entered is neither a sign nor a digit

REMEMBER: all outputs must be newline terminated

LC-3 Console Output from the machine will appear here. In the box below you can specify input Enter text beforehand, or type while the program is running. Specify bulk input by pasting Input a positive or negative decimal number (max 5 digits), followed by ENTER 7125 RO00A 10 R4 xFFF6 R110000 R2 xE42B-7125 R6XFFFF R310004 14 RZx3049 MAX_INPUT 10 (Valid input with a negative sign) LC-3 Console Output from the machine will appear here. In the box below you can specify input Enter text beforehand, or type while the program is running. Specify bulk input by pasting Input a positive or negative decimal number (max 5 digits), followed by ENTER 7125 RO00A 10 R4 xFFF6 R110000 R2 xE42B-7125 R6XFFFF R310004 14 RZx3049 MAX_INPUT 10 (Valid input with a negative sign)