name talk page 55,132 .lfcond ;list false conditionals too title 'TALK --- dumb terminal emulator' ; ; TALK --- a dump terminal emulator for the ; IBM PC, to illustrate use of the ROM BIOS ; asynchronous communications card support. ; ; Copyright (c) 1983 Ray Duncan ; May be freely reproduced for non-commercial use. ; cr equ 0dh ;ASCII carriage return lf equ 0ah ;ASCII line feed esc equ 1bh ;ASCII escape code ; echo equ 0 ;leave this zero to run ;communications full-duplex, ;change to -1 if half-duplex ; comm_port equ 0 ;set to 0 or 1 depending ;on which comm port is ;hooked to your modem ; ; cseg segment para public 'CODE' ; assume cs:cseg,ds:dseg,ss:stack ; talk proc far ;entry point from PC-DOS ; push ds ;save DS:0000 on stack xor ax,ax ;for final exit to PC-DOS. push ax ;make data area addressable mov ax,seg dseg mov ds,ax ;make sure the modem is on-line call com_stat ;by checking the "Data Set ; Ready" bit in the status word. test al,20h jnz talk1 ;if bit is on, ok to proceed. ; ;bit is not on, print warning ;message and exit. mov dx,offset msg1 jmp talk6 ; talk1: ;initialize the display to ;reverse video, so the user ;knows he's talking to the modem. ; mov ah,15 ;first use "get mode" function ;of the ROM BIOS video driver to int 10h ;find the number of columns on dec ah ;the display, save it for use ;by the screen clear routine. mov columns,ah cmp al,7 ;make sure display is text mode. je talk2 ;mode 7 ok, proceed cmp al,3 jbe talk2 ;modes 0-3 ok,proceed mov dx,offset msg2 jmp talk6 ;print error message and exit ; talk2: mov bh,70h ;now clear screen and set to call clear ;reverse video attribute 70h. ;also put the cursor in the call home ;upper left corner of screen. ; ;**************************** ;this is the main loop of ;the communications program. ;**************************** talk3: call pc_stat ;check character waiting ;from the IBM PC keyboard jz talk4 ;no call pc_in ;read char. from PC keyboard cmp al,esc ;is it the ESCape key? je talk5 ;yes, exit the terminal emulator ;if running half-duplex, echo ;the character to the PC display if echo push ax ;save copy of the character call pc_out ;send it to the PC display pop ax ;now restore the character endif call com_out ;write char. to the comm port ; talk4: call com_stat ;check if character waiting ;from the comm port jz talk3 ;no, loop call com_in ;read char. from comm port call pc_out ;write it to the PC display ; ;now do it all again jmp talk3 ; talk5: ;ESC key detected, prepare ;to exit the terminal emulator. ; ;first set the display back ;to normal video, so the user ;will know he's talking to ;the PC and not the modem. mov bh,07h ;7 is the "attribute" for call clear ;normal video display. call home ;also put cursor in upper ;left hand corner of screen. ; ;print farewell message mov dx,offset msg3 talk6: mov ah,9 ;use PC-DOS function 9 to int 21h ;print the string whose address ;is in register DX. ret ;now return to PC-DOS. ; talk endp ; ;this routine reads status ;from the COM port, returns ;Z=false if character ready ;Z=true if nothing waiting ;AH=line status,AL=modem status ;register DX destroyed. com_stat proc near mov dx,comm_port mov ah,3 ;use ROM BIOS driver's function int 14h ;3 to get status, also test ah,098h ;check comm port error flags ;for timeout,break,framing error. jnz com_err ;error was detected, beep. com_stat1: ;test the data ready bit, test ah,1 ;returning Z flag=false if ret ;character waiting. com_err: push ax ;communications error detected mov al,7 call pc_out ;send a bell code to the PC pop ax ;then go return comm status jmp com_stat1 com_stat endp ; ;read a character from the ;COM port, return it in AL. ;register DX destroyed. com_in proc near mov dx,comm_port mov ah,2 ;use ROM BIOS driver's int 14h ;function 2 to get char. ret com_in endp ; ;write the character in AL ;to the COM port. ;register DX destroyed. com_out proc near mov dx,comm_port mov ah,1 ;use ROM BIOS driver's int 14h ;function 1 to send char. ret com_out endp ; ;read status for the IBM ;PC's keyboard, returns ;Z=false if character ready ;Z=true if nothing waiting. ;register DX destroyed. pc_stat proc near ;if a character is already ;waiting,just return status mov al,in_char or al,al jnz pc_stat1 mov ah,6 ;otherwise call PC-DOS to mov dl,0ffh ;determine status int 21h jz pc_stat1 ;jump,nothing ready ;got a char, save it for ;"pc_in" routine. mov in_char,al pc_stat1: ;return to caller with ret ;Z flag set appropriately pc_stat endp ; ;read a character from the ;IBM PC's keyboard, return ;it in AL. DX may be destroyed. pc_in proc near mov al,in_char or al,al ;any character waiting? jnz pc_in1 ;yes,return it to caller call pc_stat ;try and read a character jmp pc_in pc_in1: xor ah,ah ;clear the character ;waiting flag mov in_char,ah ret ;exit with AL=char pc_in endp ; ;write the character in AL ;to the PC's display. ;register DX destroyed. pc_out proc near mov dl,al ;we use PC-DOS function 6 to mov ah,6 ;send the character, it ignores int 21h ;control characters so they ret ;can be passed on to the pc_out endp ;remote system. ; clear proc near ;clear the display and set ;it to the attribute in BH. ;registers AX, CX, DX destroyed. mov dl,columns mov dh,24 ;DL,DH=X,Y of lower right ;corner of "window". mov cx,0 ;CL,CH=X,Y of upper left ;corner of "window". mov ax,600h ;AH=6 for "scroll or initialize ;window" function, AL=0 for ;number of lines to scroll. int 10h ;call ROM BIOS video driver. ret clear endp ; ;home the cursor, i.e. ;put it in the upper left ;corner of the screen. ;registers AX,BX,DX destroyed. home proc near mov dx,0 ;(DL,DH)=(X,Y) for new ;cursor position, both are 0. mov bh,0 ;BH=video page mov ah,2 ;function 2=set cursor int 10h ;call ROM BIOS video driver. ret home endp ; cseg ends ; ; dseg segment para 'DATA' ; in_char db 0 ;PC keyboard input char. ; columns db 0 ;highest numbered column in ;current display mode (39 or 79) ; msg1 db cr,lf,'Check your modem.' db cr,lf,'$' msg2 db cr,lf,'Display must be text mode.' db cr,lf,'$' msg3 db cr,lf,lf,'Goodbye.' db cr,lf,'$' dseg ends ; ; stack segment para stack 'STACK' ;allow 64 bytes in this case db 64 dup (?) stack ends ; end talk