bogus

[ORG 0x100]

jmp @Principal

@WriteCh:

pusha
push es

mov dx, 0xB800
mov es, dx
mov cx, ax
mov al, 80
mul ah
add ax, cl
mov cx, ax
xor ax, ax
mov al, 2
mul cx
push bx
mov bx, ax
xor ax, ax
mov al, 2
mul bx
mov di, bx
xor bx, bx
pop bx
mov ah, bh
mov al, bl
stosw

pop es
popa
ret

@Principal:

mov al, 25                ;col
mov ah, 41                ;line
mov bh, 0x2F
mov bl, 'A'
call @WriteCh

@Fim:

mov ax, 0x4C00
int 0x21