segment .text
global _asm_main
 
_asm_main:
enter 0,0
pusha
 
mov dx, 0               ;send 'a' through com1
mov al, 'a'
mov ah, 1
int 14h
 
mov ah,3               ;check serial port status
int 14h                   ;to check if data is available
 
shr ax,9               ;puts bit8 to the carryflag
jc fetch                 ;if bit8=1, fetch
jnc cont               ;data is not available
 
fetch:
mov dx, 1            ;receives 'a' from com2
mov ah, 2
int 14h
 
mov dl, al            ;prints the received charac
mov ah, 02h
int 21h
 
cont:
popa
mov eax, 0
leave
ret

segment .text
global _asm_main
 
_asm_main:
enter 0,0
pusha
 
mov dx,0   ;send 'a' through com1
mov al,'a'
mov ah,1
int 14h
test ah,80h ;got this thing from ArtofASM
jnz error
 
error:
mov ah,02
mov dl,'e'
int 21h
 
popa
mov eax,0
leave
ret

%define port1 3f8h
 
segment .data
char dw 'a', 0
format dw "%s", 0
 
segment .text
global _asm_main
extern _outportb, _inportb, _printf
 
_asm_main:
enter 0,0
pusha
 
push char ;send character to port1
push port1
call _outportb
add esp, 8
 
push port1 ;receive char from port1
call _inportb
add esp, 4
 
;mov edx, eax ;print received char
;mov ah, 02h ;using assembly
;int 21
 
; i tried either way, it's not working
 
push eax ;print using printf
push format
call _printf
add esp, 8
 
popa
leave
mov eax, 0
ret

#include <stdio.h>
#include <dos.h>
 
int main()
{
int ret_status;
ret_status = asm_main();
return ret_status;
}