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Hello. I try to compare the next expressions:
1)
mov al, 4
mov bl, 12
sub al, bl ; CF == 1
0000 0100 (4)
+
1111 0100 (-12)
[bits 16] ; use 16 bits
[org 0x7c00] ; sets the start address
init:
mov si, msg ; loads the address of "msg" into SI register
mov ah, 0x0e ; sets AH to 0xe (function teletype)
print_char:
lodsb ; loads the current byte from SI into AL and increments the address in SI
cmp al, 0 ; compares AL to zero
je done ; if AL == 0, jump to "done"
int 0x10 ; print to screen using function 0xe of interrupt 0x10
jmp print_char ; repeat with next byte
done:
hlt ; stop execution
msg: db "Hello world!", 0 ; we need to explicitely put the zero byte here
times 510-($-$$) db 0 ; fill the output file with zeroes until 510 bytes are full
dw 0xaa55 ; magic number that tells the BIOS this is bootable
===> "boot.asm:18: error: parser: instruction expected";org 0x7C00 ; BIOS loads our programm at this address
;bits 16 ; We're working at 16-bit mode here
start:
cli ; Disable the interrupts
mov si, msg ; SI now points to our message
mov ah, 0x0E ; Indicate BIOS we're going to print chars
.loop lodsb ; Loads SI into AL and increments SI [next char]
or al, al ; Checks if the end of the string
jz halt ; Jump to halt if the end
int 0x10 ; Otherwise, call interrupt for printing the char
jmp .loop ; Next iteration of the loop
halt: hlt ; CPU command to halt the execution
msg: db "Hello, World!", 0 ; Our actual message to print
;; Magic numbers
times 510 – ($ – $$) db 0
dw 0xAA55