
System Memory Controller (SMC)
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B)
201
scrub can be enabled/disabled in software. Refer to
for more
information.
3.2.5
ROM/Flash Interface
The SMC provides the interface for two blocks of ROM/Flash. Each block provides addressing
and control for up to 64MB. Note that no ECC error checking is provided for the ROM/Flash.
The ROM/Flash interface allows each block to be individually configured by jumpers and/or by
software as follows:
Access for each block is controlled by three software programmable control register bits:
an overall enable, a write enable, and a reset vector enable. The overall enable controls
normal read accesses. 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.
The base address for each block is software programmable. At reset, Block A’s base
address is $FF000000, if Bank A is less than or equal to 8MB; otherwise, it is 0xF4000000.
Block B’s base address is $FF800000.
As noted above, in addition to appearing at the programmed base address, the first 1MB
of Block A/B also appears at $FFF00000- $FFFFFFFF if the reset vector enable bit is set.
The assumed size for each block is software programmable. It is initialized to its smallest
setting at reset.
The access time for each block is software programmable.
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 half of the SMC interfaces to 8 bits. In this mode, the following rules are enforced:
only single-byte writes are allowed (all other sizes are ignored), and
all reads are allowed (multiple accesses are performed to the
ROM/Flash devices when the read is for greater than one byte).
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