4020 SX  (250-4902/3)   Installing a Parallel Device    Faxback Doc. # 1613

The 25-pin parallel port is located on the back of your compute.  The
parallel port on the computer allows either one-way or two-way data
transfer:

*  UNIDIRECTIONAL (one way).  The computer uses the port only to send
        output to the parallel device.  The computer does not receive
        input through the port.
*  BIDIRECTIONAL (two-way).  The computer uses the port both to send
        output to the parallel device and to receive input from the
        device.

MS-DOS uses unidirectional or bidirectional transfer. OS/2 and SCO XENIX
uses unidirectional transfer only.

DIP Switch 5 is designed to let you control data transfer of the parallel
port.  For unidirectional transfer, set Switch 5 to ON (default).  For
bidirectional transfer, set Switch 5 to off.

Switch 5 should always be set to ON, unless the system is running under
MS-DOS and you want to use bidirectional mode.