I've been tried over and over to get this code working correctly but it 
doesn't. So i ask to any guru of modems programming to help me to find what 
wrong i did. Currently you need to change INTNUM, UART_BASE and OFFMASK to
reflect your com setting.
seg_a           segment byte public 'seg_a'
                assume  cs:seg_a, ds:seg_a, ss:seg_a
         org  100h
UART_BASE = 03E8h            ; COM1: 3F8h etc...
INTNUM      equ 74h          ; COM1; 0Ch COM2: 0Bh COM3: 0Ch COM4: 0Bh
OFFMASK     equ 00010000b    ; COM1; COM2: 00001000b
ONMASK      equ not OFFMASK
UART_RATE   equ 12           ; 9600 bps, see table in this file
UART_PARAMS equ 00000011b    ; 8n1, see tables
RXFIFOSIZE  equ 8096         ; set this to your needs
TXFIFOSIZE  equ 8096         ; dito.
start:         mov ah,35h
               mov al,INTNUM         ; irq12 
               int 21h
               mov oldirq+2, es
               mov oldirq, bx
               mov ah,25h
               mov al,INTNUM         ; irq12
               mov dx,offset newirq
               int 21h
             ; initialize the UART
               cli
               mov  dx,UART_BASE+3          ; 03EBh
               mov  al,80h                  ; set DLAB
               out  dx,al
               mov  dx,UART_BASE            ; 03E8h
               mov  ax,UART_RATE            ; 9600 bps
               out  dx,ax                   ; write bps rate divisor
               xor  ax,ax
               inc  dx
               out  dx,al                  ; set baud rate divisor high byte
               mov  dx,UART_BASE+3         ; 03EBh
               mov  al,UART_PARAMS         ;set to 8N1
               out  dx,al                  ; write parameters
               mov dx,03EFh
               in al,dx
               mov al,0f0h
               out dx,al
               in al,dx
               mov al,00h
               out dx,al
               mov  dx,UART_BASE+4          ; MCR
               xor  ax,ax  ; clear loopback
               out  dx,al
             ; is it a 16550A?
;              mov  dx,UART_BASE+2
;              in   al,dx                   ; IRR
;              and  al,11000000b
;              cmp  al,11000000b
;              jne  iu_nofifos
;              mov  bitxfifo,16
               mov  dx,UART_BASE+2          ; FCR
               mov  al,11000111b            ; trigger level 14 bytes RX
               out  dx,al  ; clear and enable the fifos if they exist
;            iu_nofifos:
               mov  dx,UART_BASE+1
               mov  al,00001101b  ; allow RX interrupts
 ;                                  enable line status interrupt
 ;                                  enable modem-status interrupt
               out  dx,al
               mov  dx,UART_BASE
               in  al,dx  ; clear receiver
               mov  dx,UART_BASE+5
               in  al,dx  ; clear line status
               inc  dx
               in  al,dx  ; clear modem status
             ; and enable ints from the UART
               mov  dx,UART_BASE+4
               mov  al,00001000b       ; enable interrupts and force dtr
               out  dx,al
               in al,0a1h
               and al,ONMASK
               out 0a1h,al          ; free interrupt in the ICU
               sti                  ; release interrupts if any
               mov dx,offset red    ; paragraph
               mov cl,04h
               shr dx,cl
               inc dx
               cmp dx,0011h
               jnb exit1
               mov dx,0011h
    exit1:     mov ah,31h
               int 21h
newirq         proc near
               push bx
               push ax
               push dx
               push si
int_loop:
              mov  dx,UART_BASE+2  ; IIR
              xor  ax,ax
              in   al,dx           ; check IIR info
              test al,1            ; interrupt pending?
              jnz  int_end         ; jump if no int. pending
              and  ax,6
              mov  si,ax
              call word ptr cs:int_servicetab[si]
              jmp  int_loop
     int_end: jmp no_ring
int_modem      proc near
               mov dx,UART_BASE+6      ;  03EEh
               in al,dx                ; read MSR  (lowest priority)
               and al,04h              ; mask ring indicator (RI) changed
               cmp al,04h
               jne by_pass
               inc byte ptr cs:[ring]
      by_pass: ret
int_modem      endp
int_tx         proc near
              ; transmit routine not used.
               ret
int_tx         endp
int_rx         proc near
get_me:        mov dx,UART_BASE       ; 03E8h  read it fast
               in al,dx
               mov bx,offset cs:mess
               add bx,word ptr cs:[pointer]
               mov byte ptr cs:[bx],al
               cmp byte ptr cs:[pointer],08h
               je ugc_nochar
               inc cs:[pointer]
   ugc_nochar: mov dx,UART_BASE+5           ; 03edh
               in al,dx
               test al,01h
               jnz get_me     ; ugc_nochar
               ret
               test ah,0eh
               jz no_error
               test ah,02h
               jz no_overrun
               mov cs:[over],01h
 no_overrun:   test ah,04h
               jz no_parity
               mov cs:[over],02h
no_parity:     test ah,08h
               jz no_framing
               mov cs:[over],03h
no_framing:
  no_error:    ret
int_rx         endp
line_status_int proc near
                mov dx,UART_BASE+5  ; 03EDh
                in al,dx            ; clear the status
                ret                 ; just read it only! and return
line_status_int endp
no_ring:
               pop si
               pop dx
               pop ax
               pop bx
               mov  al,20h ; acknowledge interrupt
               out  20h,al
               out 0a0h,al ; comment out this line if using lower irq level 
               iret
db 0eah
oldirq         dw 0
               dw 0
newirq         endp
ring           db 00h
pointer        dw 0000h
mess           db 00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,66h
over           db 00h
int_servicetab    DW int_modem, int_tx, int_rx, line_status_int
red             equ $
seg_a           ends
                end     start
--- Renegade v5-11 Exp
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