Help with getting a MARIE Assembly Program to Run Properly: I have to create a M

Question

Help with getting a MARIE Assembly Program to Run Properly:

I have to create a MARIE Assembly Program that takes in a user's input, which the input phase is halted by a "." and rotates the ASCII characters of the user's input by 13 spaces and then outputs the shifted ASCII characters.

Need Help with:

        1) So far I created the loop that can take in the input ASCII characters, but cannot seem to grab all the letters that were inputted, my code just grabs the "."

         2) Need help with deciding which variable I need to Load before calling the ROT13 subroutine

          3) Need help with verifying the ROT13 subroutine is working properly

          4) Need help with verifying my output loop is printing the correct letters

    ORG       100       / Start the program at location 100 hexadecimal

   Load       Start       / Initialize character pointer to start of block
  
UserI,   Input
   Store       Ptr
   Load       Ptr
   Subt       ChPe
   Skipcond   400
   Jump       UserI
  

   LoadI       Ptr       / Put 'A' in AC
   Store       InVal       / Store value to be transformed into InVal
   Jns       ROT13  
   Jump       OCycle               / Jump to the ROT13 subroutine
                   / Upon return, the transformed character is in AC
ROT13,   HEX       0
   Load       InVal       / Get character
   Add       Val13       / Add 13
   Store       Hold       / Save it
   Subt       ChZ       / Check if modulo adjust is needed (past 'Z')
   Skipcond   800       / No adjust needed if past 'Z'
   Jump       NoAdj
   Add       ChA  
   Jump       Done       / Result is in AC

NoAdj,   Load       Hold  
   Store       Ptr  

Done,   JumpI       ROT13       / Return with result in AC

OCycle, LoadI       Ptr
   Store       Ptr
   Subt       ChPe
   Skipcond   400
   Jump       Cont
  

Cont,   Load       Ptr
   Output
   Load       Ptr
   Add       One
   Store       Ptr
   Jump       OCycle
   Halt
/ -----
/ Constants (the program should not write to these locations)
/ -----
ChA,   HEX       0041       / Constant value 'A' for modulo adjust in subroutine
ChZ,   HEX       005A       / Constant value 'Z' for modulo check in subroutine
ChPe,   HEX       2E       / Constant period character that marks end of input
Val13,   DEC       13       / Constant rotate value of 13 for subroutine
One,   HEX       1       / Constant value 1
Start,   HEX       200       / Constant address for start of character block

/ -----
/ Data area (these locations are for reading and writing)
/ -----
InVal,   HEX       0       / Reserved for subroutine input value
Hold,   HEX       0       / Reserved for temporary variable for subroutine
Ptr,   HEX       0       / Reserved for character pointer

Explanation / Answer

/ *****

ORG 100 / Start the program at location 100 hexadecimal

/ -----

/ Input characters, transform, and store in memory until '.' is input

/ -----

Load Start / Initialize character pointer to start of block

Store Ptr

/>>>>> Add code to accomplish the input and output phases. <<<<<

Input InVal

/>>>>> Here's an example of how subroutine ROT13 is called. <<<<<

/>>>>> We'll just transform 'A' in this example then halt. <<<<<

Load ChA / Put 'A' in AC

Store InVal / Store value to be transformed into InVal

Jns ROT13 / Jump to the ROT13 subroutine

/ Upon return, the transformed character is in AC

Halt

/ -----

/ Rotate-13 subroutine: Apply ROT13 to input character in location InVal and return in AC

/ -----

/>>>>> WARNING: This subroutine *almost* works. You need to fix a bug.

ROT13, HEX 0

Load InVal / Get character

Add Val13 / Add 13

Store Hold / Save it

Subt ChZ / Check if modulo adjust is needed (past 'Z')

Skipcond 800 / No adjust needed if past 'Z'

Jump NoAdj

Add ChA / Add 'A' back to difference to perform modulo

Jump Done / Result is in AC

NoAdj, Load Hold / No adjust needed, get result

Done, JumpI ROT13 / Return with result in AC

/ -----

/ Constants (the program should not write to these locations)

/ -----

ChA, HEX 0041 / Constant value 'A' for modulo adjust in subroutine

ChZ, HEX 005A / Constant value 'Z' for modulo check in subroutine

ChPe, HEX 2E / Constant period character that marks end of input

Val13, DEC 13 / Constant rotate value of 13 for subroutine

One, HEX 1 / Constant value 1

Start, HEX 200 / Constant address for start of character block

/ -----

/ Data area (these locations are for reading and writing)

/ -----

InVal, HEX 0 / Reserved for subroutine input value

Hold, HEX 0 / Reserved for temporary variable for subroutine

Ptr, HEX 0 / Reserved for character pointer

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