MPC555
/
MPC556
MEMORY CONTROLLER
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
10-22
• The memory controller takes control of the external access
• The attributes for the access are taken from one of the base and option registers
of the appropriate chip select
• The chip-select region selected is determined by the “CS line select” bit field
(
10.8.5 Dual Mapping Base Register (DMBR)
Note that dual mapping can operate only for addresses within the FLASH pre-allocat-
ed address (up to 2 Mbytes). This is achieved by programming only six bits for the
base address (11:16); The upper bits are always set as follows:
bus_addr[0:10]={0000000,isb[0:2],0}
Where ISB[0:2] represents the bit field in IMMR register that determines the location
of the address map of the MPC555 / MPC556.
With dual mapping, aliasing of address spaces may occur. This happens when the
user maps the dual-mapped region into a region which is also mapped into one of the
four regions available in the memory controller. If the user writes code or data to the
dual-mapped region, care must be taken to avoid overwriting this code or data by nor-
mal accesses of the chip-select region.
There is a match if:
bus_address[0:16] == {0000000,isb[0:2],0,dmbr_reg_value[1:6]}
Care must also be taken to avoid overwriting “normal” CSx data with dual-mapped
code or data.
One way to avoid this situation is by disabling the chip-select region and enabling only
the dual-mapped region (DME = 1, but Vx = 0, where x = selected region, 0.3).
illustrates the phenomena.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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