I need help writing a small assembly language program debug in DOS. The program must transmit and recieve through the serial port.
Example
int 14h; initializes serial port
Thanks.

You would want to select the parity, stop bits, and baud rate you want to use on both systems.
For word length (data bits), you can select between 7 or 8. Use 2 for 7 or 3 for 8 bits.
The lowest 2 bits of the vlue in AL when the bios function call is made will determine the word length.
Bit 2 of AL will determine the number of stop bits. 0=1, 1=2 stop bits.
Bits 3 & 4 set the parity. 00=no parity, 01=odd, and 11=even.
The high 3 bits set the baud rate. 000=110 baud. 001=150 baud. From there on up, each additional incrementation will double the baud rate, so a reasonable value might be 101 for 2400 baud. (Usually very reliable) Max value for the 8250 is 111, or 9600 baud.

So, for a wordlength of 8 bits, even parity, 1 stop bit, 2400 baud, I would do this:
PLace the wordlength of 3 into AL, OR AL with 00 (no change) for stop bits of 1, OR AL with the parity value of 18 (HEX), OR AL with A0 for baudrate.
Then I would place a zero in AH, to specify function 0 to initialize the serial port, a 0 in DX to specify COM 1 (don't remember how to choose COM 2--Maybe it's a 1).
Now I would execute interrupt 14H.

At this point the port is opened, and I can either read from it or write to it, using the correct procedure, of course.

I'll leave the transmission procedure for someone else, or another time, as I'm getting a headache just from this much.:)

See this address Maria :)

http://webster.cs.ucr.edu/Page_asm/ArtofAssembly/CH13/CH13-3.html#HEADING3-1