Using PC/X and MC/X Boards with MS-DOS Applications 

PC/X Boards 
MS-DOS application programs generally communicate with COM ports by 
directly accessing the UARTs via their I/O ports. Since these programs control 
the I/O hardware directly, no device driver is required. Some programs allow the
user to specify the I/O port address and IRQ (Interrupt Request) line for each 
port, while others are able to use only the standard PC COM ports COM1 and 
COM2 (some applications can also use COM3 and COM4). 

To use a DigiBoard PC/4 or PC/8 board with applications that allow the user to 
specify the I/O port address and IRQ line for each port, set the DIP switches
and jumpers for addresses and IRQs that are not used by any other device in the 
system, then configure the application for the same addresses and IRQs (use the 
application's setup program or configuration screens). 

To use a DigiBoard PC/4 or PC/8 board with MS-DOS applications that can 
reference only standard PC COM ports, the board must be set up to emulate 
these ports.  To do this, set the DIP switches and jumpers on the board so that 
the first two (or four) ports on the board have the same I/O addresses and 
interrupts as the standard PC COM ports, as shown below. 
 
COM Port  I/O Address    IRQ

COM1         3F8h         4
COM2         2F8h         3
COM3         3E8h         4
COM4         2E8h         3

When using a PC/X board to emulate standard PC COM ports, existing COM
ports must be removed or completely disabled.

PC/16 boards cannot be configured to emulate standard PC COM ports.

Standard COM 1-4 dipswitch settings for PC/4 and PC/8

	 COM1 - IRQ 4
	                 Switch: 1  2  3  4  5  6  7  8
  DS2   Address = 3f8        on: -  -  -  -  -  -  -  x 
       		            off: x  x  x  x  x  x  x  - 
	------------------------------------------------
	 COM2 - IRQ 3
	       	         Switch: 1  2  3  4  5  6  7  8
  DS3   Address = 2f8        on: -  x  -  -  -  -  -  x
	                    off: x  -  x  x  x  x  x  - 
	-----------------------------------------------
         COM3 - IRQ 4
	                 Switch: 1  2  3  4  5  6  7  8
  DS4   Address = 3e8        on: -  -  -  -  -  x  -  x 
	                    off: x  x  x  x  x  -  x  - 
	-----------------------------------------------  
         COM4 - IRQ 3
	                 Switch: 1  2  3  4  5  6  7  8
  DS5   Address = 2e8        on: -  x  -  -  -  x  -  x 
	                    off: x  -  x  x  x  -  x  - 

Standard COM 1-4 jumper settings for PC/4 & PC/8

J1  J3     
 |   | 
| |x| |x|  | | |	J1  2,3   even interrupt  ( IRQ 4 )
|x|x|x|x|  |x|x|        J2  1,2   odd  interrupt  ( IRQ 3 )
|x| |x| |  |x|x|        J3  2,3   even interrupt  ( IRQ 4 )
   |   |    | |         J4  1,2   odd  interrupt  ( IRQ 3 )
  J2  J4   J9 J10       J9  2,3   board 0 
                        J10 2,3   board 0

   J86 J88 J90
    |   |   | 
 |x| | | |x| |          Jumper on J85 for IRQ3
 |x| | | |x| |          Jumper on J89 for IRQ4
  |   |   |    
J85  J87  J89

Jumper on P2 -middle 2 pins   Jumper on P3 -middle 2 pins
 
MC/X Boards 
MC/X boards have a feature that allows the first port to act like COM2. This is
set during configuration with the IBM setup disk (see page 28).  When Com2 
Status is enabled, the first port on the board is assigned I/O address 2F8h and 
IRQ 3. The remainder of the ports are unaffected. 
 
If your machine has a built-in or installed COM2 port, it must be disabled or
removed if Com2 Status is enabled on the MC/X board. Failure to do this will
result in I/O and interrupt conflicts between the two devices. Similarly, only
one MC/X board may have Com2 Status enabled.