Question

a)in what format are negative numbers stored in the Marie architecture?
b)how does the decimal (base 10) number -12 appear in the MARIEsim memory display?
c)the Marie instruction format has a 4-bit opcode,leaving the room for a 12-bit operand. what limit does this place on instructions and addressable memory in MARIE?

Answer 1

a)

For 32 bit DWORD the integer range is from –2147483648 to 2147483647 or in hex -0x80000000 to 0x7FFFFFFF.

So the number -1 is present like 0xFFFFFFFF. (Like counter underflow)

If the high (31) bit is set then the number is negative. To make positive number from negative (negation) you must make compement of number and add 1.

Example:

0xFFFFFFFE //-2
xor 0xFFFFFFFF //binary complement
---------------
0x00000001 //result of complement
+ 0x00000001 //add 1
---------------
0x00000002 //Result of negation is 2

b)

.MODEL SMALL
.STACK 100H

.DATA
PROMPT_1 DB 'Enter a Decimal number (-32767 to 32767) : $'
PROMPT_2 DB 0DH,0AH,'The given Decimal number is : $'
ILLEGAL DB 0DH,0AH,'Illegal character. Try again : $'

.CODE
MAIN PROC
MOV AX, @DATA ; initialize DS
MOV DS, AX

LEA DX, PROMPT_1 ; load and display the string PROMPT_1
MOV AH, 9
INT 21H

CALL DECIMAL_INPUT ; call the procedure DECIMAL_INPUT

LEA DX, PROMPT_2 ; load and display the string PROMPT_2
MOV AH, 9
INT 21H

CALL DECIMAL_OUTPUT ; call the procedure DECIMAL_OUTPUT

MOV AH, 4CH ; return control to DOS
INT 21H
MAIN ENDP