
MOTOROLA
Chapter 10. Memory Controller
10-29
Dual Mapping of an External Flash Region
10.6 Dual Mapping of an External Flash Region
The dual mapping feature also enables mapping of external memory to alternative memory
regions controlled by the memory controller. When dual mapping is enabled and an
external address matches a dual mapped address, and the cycle type matches AT/ATM field
in DMBR/DMOR register, then the following occur:
The chip-select that is mapped to the access does not respond to that address (it
remains negated)
The chip-select region selected is determined by the DMCS bit field in the DMBR
register
The attributes for the access are taken from the corresponding chip select region
Dual mapping can only be enabled over memory addresses in the range 0x0000 0000
through 0x000F FFFF.
NOTE
Internal flash must be disabled to use dual mapping over an
external memory.
10.7 Global (Boot) Chip-Select Operation
Global (Boot) chip-select operation allows address decoding for a boot ROM before system
initialization. If the global chip-select feature is enabled then the memory controller is
enabled from reset.
The global chip select port size is programmable at system reset using the BPS pins (pins
[4:5]) of the reset configuration word (RCW). The global chip select does not provide write
protection and responds to all address types, allowing a boot ROM to be located anywhere
in the address space.
The memory controller will operate in this boot mode until the first write to any chip select
option register (ORx).The chip select pin can be programmed to continue decoding a range
of addresses after this write, provided the preferred address range is first loaded into the
chip select base register (BRx). After the first write to ORx, the global chip select can only
be restarted with a system reset.
Which chip-select line is used as the global chip select, and how it operates, is determined
by the reset configuration parameters
FLEN – Internal Flash Enable (bit 20)
BDIS – Boot Disable (bit 3)
DME – Dual Mapping Enable (bit 31)
Table 10-4 summarizes global chip select operations for all combinations of values on these
reset configuration word lines.