
EPC-7 Hardware Reference
set for every access using the E-page window. Make sure that those registers not
directly supplying address lines are set to "FF" values in the appropriate bit positions.
Direct VMEbus Accesses
An alternate way to perform VMEbus accesses, providing that the EPC-7 is running
in protected mode is to perform reads and writes at 486 addresses above 10000000h
(256 MB). For instance, a 4-byte read at address 40000000h will result in a 4-byte
VMEbus read access at address 00000000 with an address modifier specifying A32,
supervisory data and no byte-swapping (little-endian mode).
With the EPC-7, addresses above 256 MB, with one exception for PC compatibility,
map onto the VMEbus. When direct "protected-mode" addressing of A24 or A16
space, the high-order nibble is used to define the access mode and byte ordering. For
A32 space, the high-order 2 bits define the access mode leaving 30 bits available for
addressing. Thus, only the first 1 Gigabyte of VMEbus A32 space is directly
addressable. All A24 and A16 space is directly addressable. The chart following
shows how this direct mapping is used.
7
7
Address Range
Access Mode
Byte Order
1xxx0000 - 1xxxFFFF VME A16 supervisory data
little endian
2x000000 - 3xFFFFFF VME A24 supervisory data
little endian
40000000 - 7FFFFFFF VME A32 supervisory data
(mapped to VME 00000000-3FFFFFFF)
little endian
80000000 - BFFFFFFF VME A32 supervisory data
(mapped to VME 00000000-3FFFFFFF)
big endian
Cxxx0000 - DxxxFFFF VME A16 supervisory data
big endian
Ex000000 - ExFFFFFF VME A24 supervisory data
big endian
F0000000 - FFFEFFFF Mapped to EXM expansion interface
FFFF0000 - FFFFFFFF 486 upper ROM area
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