Reference no: EM133860453

Question

You are to design, write, test, and debug a MARIE assembly language program that inputs a sequence of characters from the set A-Z (capital letters only), stores each character in memory after it is transformed by the trivial ROT13 cipher, and then, after character input completes, outputs the transformed characters.

A template source code file (Project-2_Starting_Code.mas) is provided with this assignment. Edit this file to create a program that meets the program specifications. Note that the template includes instructions to initialize some working values that your program can use. The template also defines memory locations.

You may add data memory locations. The program can be designed without additional data locations, but it may be necessary to do so for your design.

For full credit, your solution must perform the functions and satisfy the requirements specified below.

a) The first instruction of the program must be placed at location (address) 0x100 (100 hexadecimal) in MARIE's memory. This is accomplished by following the program template that is provided.

b) The constant data values (One, ChA, ChZ, ChPe, Val13, Start) should not be changed by the program. The program can load from these memory locations, but should not store to them.

c) Transformed input characters must be stored in successive memory locations beginning at location 0x200 (200 hexadecimal) as indicated in the program template. The program should store all transformed input characters before any characters are output.

d) The program should always initialize the values for Ptr in the working data memory and not rely on the values for these locations that are defined in the assembly source file. This initialization is done by the provided template file.

e) The program should work for any inputs 'A' through 'Z' and '.' (a period terminates input). In the interest of keeping the program simple, the program does not need to validate inputs.

f) When transformed characters are stored and when transformed characters are output, the program must use a loop and indirect addressing to access the values in the array of words. Note that variable Ptr is initialized in the template code and should be used in the loop. You may also define a Count variable to count the number of characters, but there are also correct designs that do not require a Count variable.

g) The program should operate as follows:

Input Phase:

1. A character (A-Z or '.') is input. MarieSim allows the user to input a single character that is read into the accumulator (AC) with an Input instruction.

2. If character '.' (period) is input, then the input phase ends and the output phase begins (step 5 below). (The period may be stored in memory to mark the end of the characters or the characters can be counted to determine how many transformed characters to output during the output phase.)

3. The character that is input is transformed using the trivial ROT13 cipher (see Section 5.1).

4. The transformed character is stored in the next location in the block of memory beginning at location Start. (Variable Ptr must be updated and indirect memory addressing must be used.)

Output Phase:

5. All transformed characters are output, beginning with the first character that was transformed.

The '.' character is not to be output. (This will require a loop using variable Ptr and indirect addressing. Note that the number of characters to output will vary and the program must know when to stop the output by relying on a '.' or other special character in memory, counting the
number of input characters during the input phase, or some other method.)

6. After all characters are output, the program halts by executing the HALT instruction.

4. Testing

Test and debug the program using the MARIE simulator. Debug the program using the "Step" and "Breakpoint" (step-by-step) features of the simulator. You must test your program with the following two test cases.

Test 1: Input the eight-character sequence "VIRGINIA" followed by a '.' to terminate the input. Note that you need to input one character at a time into MarieSim's UNICODE Input area, with each character followed by pressing the "Enter" key. The ROT13 value of each character ("IVETVAVN") should be displayed after the '.' character is input.

Test 2: Rerun the program in MarieSim, without reassembling or reloading, then input the four-character sequence "GRPU" followed by a '.' to terminate the input. Note the output.