Appendix
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Memory Conflicts
73
COM/Xi Issues
The COM/Xi board has 256K of on-board RAM which can be accessed by the
host computer through a 32K window on the host’s memory bus. The
COM/Xi’s 32K window can be mapped into one of four address ranges on the
host memory bus: C0000h-C7FFFh, C8000h-CFFFFh, D0000h-D7FFFh or
D8000h-DFFFFh. Contingent upon the availability of these address ranges, up
to four COM/Xi boards can be installed in a host computer (each COM/Xi board
requires its own 32K block of addresses).
Typical sources of contention and possible solutions are:
•
Plug-in VGA and EGA cards, which have a ROM BIOS beginning at
C0000h Solution: Remove the VGA or EGA card from the system and use a
Monochrome Display Adapter instead.
•
ESDI hard disk controllers, which typically have a ROM BIOS beginning at
C8000h or CC000h Solution: Replace the ESDI drive and controller with an
MFM drive and controller.
•
SCSI interfaces, which have a ROM BIOS that may be located anywhere in
the C0000h-DFFFFh range Solution: Remove or relocate the SCSI interface.
In most cases, resolution of a memory contention problem involves a sacrifice.
The more COM/Xi boards you try to put in a host computer, the more likely it is
that contention will result. Another alternative, if it is necessary to have a large
number of ports, is to switch to the DigiBoard PC/X* (PC/Xe and PC/Xi) line of
boards. While the PC/X* boards need a minimum memory address space of
64K, up to four boards can be stacked in the same address range, and the
boards are available with up to 16 ports each, giving you a total of 64 ports.
