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DigiBoard Intelligent Serial Communications Boards
Jumper Settings
The COM/Xi Processor board has three sets of jumpers which determine the I/O
port address, the interrupt request (IRQ) line and the starting address of the
board’s dual-ported memory window. See your software installation instructions
for recommended address and IRQ selections.
Memory Start Address—Jumpers J15, J16 and J17
The COM/Xi board has 256K of on-board RAM which is accessible to the host
computer through a 32K “window” in the host’s memory map. The 32K
window is mapped into an unused block of memory address space in the area
reserved for expansion boards (0C0000h-0DFFFFh). There are four address
ranges available for the COM/Xi: 0C0000h-0C7FFFh, 0C8000h-0CFFFFh,
0D0000h-0D7FFFFh and 0D8000h-0DFFFFh. Each COM/Xi board requires its
own 32K block of addresses, and no other device may share these addresses.
While up to four COM/Xi boards can be installed in a system, this assumes that
the entire 128K from 0C0000h-0DFFFFh is available. In practice, this is often
not the case. EGA and VGA cards use memory addresses in this region, as do
ESDI and SCSI controllers. Also, the presence of 16-bit memory devices (such
as 16-bit VGA cards) in this region can cause COM/Xi boards to fail. See the
Appendix, starting on page 68, for a more detailed discussion of potential
memory conflicts and ways to resolve them.
Figure 14 shows the jumper settings for the four memory start addresses
available on the COM/Xi board.
Figure 14
J15-J17—COM/Xi Memory Start Addresses
J15
J16
J17
0C0000h
J15
J16
J17
0C8000h
J15
J16
J17
0D0000h
J15
J16
J17
0D8000h
See the Appendix for information about memory conflicts.
