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; Lab 1
; assignment: develop a code to print a value stored in a register
;             as a hexadecimal number to the monitor
; algorithm: turning each group of four bits into a digit
;            calculate the corresponding ASCII character;
;            print the character to the monitor
; Hint: Shift left is a multiply by 2

; R0 OUT Trap Register
; R1 Branching purposes
; R2 Digit Counter
; R3 Data
; R4 Digit
; R5 Bit Counter

.ORIG x3000

LD R3, REGISTER_3

AND R2, R2, #0
ADD R2, R2, #3
TOP_OF_HEX_LOOP
BRn FINISHED
AND R4, R4, #0
AND R5, R5, #0
ADD R5, R5, #3

TOP_OF_BIT_LOOP
BRnz TOP_OF_PRINT
ADD R4, R4, R4
; Is R3 < 0?
AND R1, R1, #0
NOT R1, R3
BRzp SKIP_ADD
ADD R4, R4, #1

SKIP_ADD
ADD R3, R3, R3
ADD R5, R5, #-1
BRnzp TOP_OF_BIT_LOOP

TOP_OF_PRINT
AND R1, R1, #0
ADD R1, R4, #-9
BRnz ADD_ZERO
BRp ADD_A_MINUS_10

ADD_ZERO
ADD R4, R4, #15
ADD R4, R4, #15
ADD R4, R4, #15
ADD R4, R4, #3
BRnzp PRINT

ADD_A_MINUS_10
ADD R4, R4, #31
ADD R4, R4, #15
ADD R4, R4, #9
BRnzp PRINT

PRINT
AND R0, R0, #0
ADD R0, R4, #0
OUT
ADD R2, R2, #-1
BRnzp TOP_OF_HEX_LOOP

FINISHED
; stop the computer
HALT

; program data section starts here

REGISTER_3 .FILL x00E0

.END