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Register Descriptions Chapter 4
VXI-MXI User Manual 4-14 © National Instruments Corporation
A16 Window Map Register
VXIbus Address: Base Address + C (hex)
Attributes: Read/Write
This register defines the range of addresses in the lower 48 KB of A16 space that is mapped into
and out of the VXI-MXI through the MXIbus. Earlier versions of the VXI-MXI required the
A16 window to be statically configured with a DIP switch. Now the A16 window can only be
dynamically configured with this register. These bits are cleared on a hard reset.
The CMODE bit in the MXIbus Control Register selects the format of this register. If the
CMODE bit is 0 (default), a Base/Size window comparison is used to determine the range of
addresses in the window. If the CMODE bit is set, an upper and lower bound is used to
determine the range of addresses in the window.
The A16 Window Map Register has the following format when the CMODE bit is cleared:
R
15 14 13 12 11 10 9
0
A16EN A16DIR 1 1 A16SIZE2 A16SIZE1 A16SIZE0
8
0
A16EN
00
A16SIZE0
W
A16DIR A16SIZE2 A16SIZE1
7
654321
A16BASE7 A16BASE6 A16BASE
5
A16BASE4 A16BASE
3
A16BASE
2
A16BASE1 A16BASE0
0
R/W
Bit Mnemonic Description
15r/w 0 Reserved Bit
This bit is reserved and reads back as zero. Write a zero when
writing to these bits.
14r/w A16EN A16 Window Enable Bit
When this bit is set, the A16 mapping window is enabled. When
this bit is cleared, the A16 mapping window is disabled.
13r/w A16DIR A16 Window Direction Bit
When this bit is set, the A16 window applies to MXIbus cycles that
are mapped into VXIbus cycles (inward cycles). When this bit is
cleared, the A16 window applies to VXIbus cycles that are mapped
out into MXIbus cycles (outward cycles). The complement of the
defined range is mapped in the opposite direction.