9086/system/boot_code.asm

.ORG 0x84           ; INT 21
DW 0xFFFF           ; Code Segment
DW PRINT_INT_HANDLE ; Program Counter

.ORG 0x0100
start:
MOV SP,#STACK
MOV AX,#0x0000
MOV CX,#0x0000
MOV BX,#0x0000
CALL TEST_
ADD CX,#0xBEEF
ADD CX,#0x4111
mov AX,#0x00FF
inc AL
mov AX,#0x00FF
inc ax
ADD AX,#0x2200
MOV SI,#0x0101
MOV [SI],AX
inc [si]
inc [si]
inc [si]
dec [si]
dec cx
cmp CX,#0x00
MOV CH,#0x9A
inw #0x20
CMP AL,#0xCD
jz WAZZ
mov al,#'0
out byte #0xA5
hlt
WAZZ:
CMP AH,#0xAB
jz WAZZ2
mov al,#'0
out byte #0xA5
hlt
WAZZ2:
mov al,#'1
outb #0xA5
hlt
TEST_:
ADD AX,#0xDEAD
RET

;quick&dirty
PRINT_INT_HANDLE:
push AX
MOV AL,DL
out byte #0xA5
POP AX
iret

 .BLKB 10
STACK:

.ORG 0xFFF0
MOV AX,#0x0100
JMP AX