title   Processor to turn off COM DTR   
;   
;          This program turns off the DTR signal on the communications  
;     port of a Zenith Z100 micro.  This makes the Z100 compatible  
;     with the Gandalf PACX communications switch.  The execution   
;     of this program should be the FIRST thing in the AUTOEXEC.BAT 
;     file.  It MUST be before the DATE & TIME calls.   
;   
;          This program is necesary because the vanila ZDOS leaves  
;     the DTR signal on after a reset or boot.  A preferable
;     solution would be to fix ZDOS, but this works too.  Note that 
;     in either case it is the user's terminal emulator's resposibility 
;     to insure that DTR is raised at the beginning of a session AND
;     lowered at the end.   
;   
;          Mitch Blank  
;   
        name    OFF 
code    segment byte    public  'code'  
        assume  cs:code,ds:code,es:code,ss:code 
        org     100h
start:  mov     al,4            ; Turn off DTR & RTS
        out     0EFh,al 
        int     20h 
code    ends
        end     start