BVME4000/6000
46
Copyright
1993,1995,1998,2001 BVM Ltd.
7.10.3 Short I/O (A16) Accesses
The BVME4000/6000 will respond to Short I/O (A16) accesses. The size of the window is fixed at
256bytes. The base address is programmable on 256byte boundaries.
Short I/O space accesses act as a location monitor only and do not access physical memory within the
BVME4000/6000. This space is used to allow 'mail box' interrupts to the processor on the
BVME4000/6000. This allows other bus masters to use semaphore control with the BVME4000/6000
without the use of the VMEbus IRQ lines.
The BVME4000/6000 responds to the following A16 Address Modifiers (AM) codes:
CPU Supervisor
Data Access
=
$2D
CPU User
Data Access
=
$29
7.10.4 Controlling The Window Size
The table below shows window sizes for valid combinations of the Mask Register:
Mask Register
A24 Address Space Window Size
A32 Address Space Window Size
00
64Kb
16Mb
01
128kb
32Mb
03
256kb
64Mb
07
512Kb
128Mb
0F
1024Kb
256Mb
1F
2048Kb
512Mb
3F
4096Kb
1024Mb
7F
8192Kb
2048Mb
FF
16384Kb
4096Mb
7.10.5 Local Address Generation
The two Local Base Address registers (A32LBA and A24LBA) contain the base address of the 'dual
mapped' memory window.
For A32 accesses, the unmasked (see A32MSK register description) A32 Local Base Address
(A32LBA) Register bits are used as the most significant address lines during the VMEbus slave
access to the onboard memory. All other local address lines are driven from the VMEbus Address bus.
For A24 accesses, The most significant eight local address lines are driven by the
A32LBA
register.
The unmasked (see A24MSK register description) A24 Local Base Address (A24LBA) Register bits
are used as the next most significant address lines during the VMEbus slave access to the onboard
memory. All other local address lines are driven from the VMEbus Address bus.
Thus for standard (A24) VMEbus accesses both the A32LBA and the A24LBA registers need to
be set up.
Содержание BVME4000
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