51b

	.MODEL TINY
	.386

	.CODE
	ORG 100h

start:	jmp main


COMM_INIT	EQU 0
COMM_EXIT	EQU 1
COMM_SEND	EQU 2
COMM_RCV	EQU 3


rs232	STRUCT

	portadr 	dw ?
	irq		dw ?
	baudrate	dw ?
	parity		dw ?
	wordlen 	dw ?
	stopbits	dw ?

rs232  ENDS

rs	rs232 <>


no_comm 	db 'No RS-232 driver found!', 13, 10, '$'

main:
	push	cs
	pop	ds

	mov	ax, 0
	mov	es, ax
	mov	dx, es:[180h]
	shl	edx, 16
	mov	dx, es:[182h]
	cmp	edx, 0
	jnz	comm_installed_ok

	mov	ah, 9
	mov	dx, offset no_comm
	int	21h
	jmp	err_exit


comm_installed_ok:

	mov	ah, COMM_INIT		;Initialize comm port

	mov	rs.portadr, 02f8h
	mov	rs.irq, 3
	mov	rs.baudrate, 9600
	mov	rs.parity, 0
	mov	rs.wordlen, 8
	mov	rs.stopbits, 1
	push	cs
	pop	es
	mov	di, offset rs

	int	60h


comm_lp:
	mov	ah, COMM_RCV		;Check if byte available from comm
	int	60h			;port
	cmp	ax, 0			;No, check if key pressed
	jz	chk_key

	mov	ah, 2			;Yes, write byte to screen
	mov	dl, al
	int	21h

chk_key:
	mov	ah, 1
	int	16h
	jz	comm_lp

	mov	ah, 0
	int	16h
	cmp	al, 27
	jz	rdy

	mov	ah, COMM_SEND		;Send byte to comm port
	mov	dx, ax
wait_cts:
	int	60h
	cmp	ax, 0
	jnz	comm_lp
	mov	ax, dx
	jmp	wait_cts

rdy:
	mov	ah, 1
	int	60h
err_exit:
	mov	ax, 4c00h
	int	21h


	END start
.

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