Functional Description
http://www.motorola.com/computer/literature 3-19
3
vector enable. The overall enable controls normal read acesses. The
write enable is used to program Flash devices. The reset vector
enable controls whether the block is also enabled at $FFF00000 -
$FFFFFFFF. The overall enable and write enable bits are always
cleared at reset. The reset vector enable bit is cleared or set at reset
depending on external jumper configuration. This allows the board
designer to use external jumpers to enable/disable Block A/B
ROM/Flash as the source of reset vectors.
2. The base address for each block is software programmable. At reset,
Block A’s base address is $FF000000 and Block B’s base address is
$FF400000.
As noted above, in addition to appearing at the programmed base
address, the first 1Mbyte of Block A/B also appears at $FFF00000-
$FFFFFFFF if the reset vector enable bit is set.
3. The assumed size for each block is software programmable. It is
initialized to its smallest setting at reset.
4. The access time for each block is software programmable
5. The assumed width for Block A/B is determined by an external
jumper at reset time. It also is available as a status bit and cannot be
changed by software.
When the width status bit is cleared, the block’s ROM /Flash is
considered to be 16 bits wide, where each Falcon interfaces to 8 bits.
In this mode, the following rules are enforced:
a. only single-byte writes are allowed (all other sizes are ignored),
and
b. all reads are allowed (multiple accesses are performed to the
ROM/Flash devices when the read is for greater than one byte).
When the width status bit is set, the block’s ROM/Flash is
considered to be 64 bits wide, where each Falcon interfaces with 32
bits. In this mode, the following rules are enforced:
c. only aligned, 4-byte writes should be attempted (all other sizes
are ignored), and
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