Accessing Vmebus Memory Space Using The Real Mode Window; Eprom; Vmebus Lack Space - Xycom XVME-678 Manual

XVME-678/688 Manual
July 1994
4.3 ACCESSING VMEbus MEMORY SPACE USING THE REAL MODE WINDOW
The Real Mode Window is 64 Kbytes long and resides within addresses OEOOOO-OEFFFF. It provides a
means of addressing the VMEbus Short 110 and Standard memory spaces. The window can be software
configured to address one of four entities: VMEbus Short 110 space, VMEbus Standard address space,
VMEbus lACK space, and EPROM.
The window is controlled by bits 5 and 6 of Control Register 1 (see Section 4.6.1). The next four sections
describe how the window operates for each configuration.
4.3.1 EPROM
This mode is selected after reset and is compatible with the IBM PC/AT architecture. When the window
is configured for EPROM, the off-board EPROM (if one exists) appears in the window. The on-board
EPROM is only accessed under the following two conditions:
• Bits 05 and 06 in Control Register
1
are set to
0
to allow an EPROM access.
• The on-board EPROM is enabled through the Extended BIOS Setup Menu (see Section 3.3.1 for
more information).
NOTE
To access the VMEbus, bit 0 of Control Register 3 must be set to
o.
4.3.2 VMEbus lACK Space
When the window is configured for the VMEbus lACK space, a byte read from specific addresses within
the window causes the XVME-678/688 to perform a VMEbus lACK cycle. The data returned from the
byte read is the status 10 vector returned from the responding VMEbus interrupter.
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