I'm using dosbox to allow 16 bit programs to run and TASM. my OS is windows 8 and I don't seemm to have any trouble with running any other interrupts except the 14h interrupt specifically transmit and receive. I use two USB to UART modules with their RX and TX tied to one another (rx->tx, tx->rx) and their grounds are connected as well. My problem is that it just won't transmit. The modules are fine as I tested them both with realterm.
here's my code for transmit.
.model small
.stack
.data
.code
main proc far
mov ax,@data
mov ds,ax
mov al,11100011b ;baud rate set to 9600
mov dx,0 ;com port 1, yes i've configured the comport on both pc and conf file of dosbox
int 14h
mov ah,01
mov al,42h ;character to transmit, letter B
mov dx,0h
int 14h
mov ah,4ch
int 21h
main endp
end main