DUALPORT.DOC

                 Using Kaypro's to demo software
                        02/22/84  D. Berg

     Recently  I was asked if there was a way to set up  multiple 
displays using Kaypro computers at the user group meetings.   One 
computer  was to run a software demo and the other units were  to 
simply display a copy of what was on the main unit.  After giving 
the problem a little thought this is what I came up with.

     First  a program would be needed in the main "demo" unit  to 
catch  the  characters going to the screen and pass them  to  the 
serial  port  where the remote displays could  read  them.   This 
program would need to fit in the machine in a manner such that it 
would  not  interfere  with normal operations - but  would  catch 
everything going to the screen.   Then a cable(s) would be needed 
to connect the main unit with the display units.  And finally the 
display  units would need to have a terminal program  running  in  
them - like TERM.COM.

     Operating  procedures  for the setup above are  as  follows:  
The  computers are set-up and connected with the cable (described 
later).   The  baud rate would be set to 9600 baud and  the  TERM 
program run.   These units will now function as display monitors.  
The  main-demo unit is booted and the DUALPORT program  run.   It 
sets  the unit to 9600 baud and patches the I/O to go to both the 
screen and the serial port.  DUALPORT will remain in effect until 
the system is powered off or the reset button is pressed.  CTRL-C 
will not affect the operation however.

     The cable needed in this setup is simple requiring only  two 
wires  be hooked up between the units.   Refering to the  diagram 
below  the HOST unit is the main demo unit and the REMOTE unit is 
the  display units.   Multiple display units can be connected  in 
parallel  qith each other.   There is a limit to the number  that 
will work but it should handle up to 6 units.   On all connectors 
pins 5,  6,  and 8 are connected together on that connector only.  
Pin 7 of all connectors are connected together in parallel.   Pin 
2 of the HOST connector is connected to all pin 3's of the remote 
connectors.   This  forms a one-way communications link from  the 
HOST to all the REMOTE units.

          HOST                           REMOTE
        --------                        --------
           1                                1
           2--------------+                 2
           3              +---------+-------3
           4                        !       4
       *---5                        !       5---*
       *---6                        !       6---*
       !   7--------------------+-- ! ------7   !
       *---8                    !   !       8---*
                                V   V
                            To other REMOTE
                            display units.