AN2866 Freescale Semiconductor / Motorola, AN2866 Datasheet - Page 24

• Manufacturer Part Number: AN2866
• Description: Migrating from the MC68332 to the ColdFire MCF523x
• Manufacturer: Freescale Semiconductor / Motorola

Device Differences
2.6
2.6.1
The fact that the MCF523x supports 32-bit addressing and the MC68332 supports 24-bit addressing should
make no difference when porting the system software, because the MCF523x can use a 24-bit addressing
scheme. This is accomplished by treating the upper 8-bits as a “don't-care” (except when using on-chip
cache). The MCF523x has three registers that control how specific regions of address space are assigned
access control attributes: two access control registers (ACR0 and ACR1) and the cache control register
(CACR). Since the ACRs and the CACR use address bits 31–24 to define reference attributes for memory
regions, virtual-to-physical memory mapping can be used to map unique 24-bit address space regions to
unique 16-Mbyte regions in the 32-bit address space. This will enable certain areas of the physical memory
map to utilize the capabilities of MCF523x caching. For instance, this can be accomplished by
concatenating A[31:24] = $01 in front of the first 24-bit address region, and using ACR0 to control the
caching scheme for this region. This can also be done for ACR1 and CACR to configure cacheable
memory regions. For more details, please refer to Chapter 5, “Cache,” of the MCF5235 Reference Manual.
24
Software Considerations
Mapping 24-bit MC68332 Addresses to the
32-bit MCF523x
Inputs
driven
high or
low as
needed
Figure 4. MCF523x Recommended Reset Configuration Circuit
Migrating from the MC68332 to the ColdFire
74HC244
V
DD
/V
SS
OE
®
MCF523x, Rev. 1.0
D16
D17
D19
D20
D21
D24
D25
RSTOUT
RCON
CLKMOD0
CLKMOD1
JTAG_EN
MCF523x
Freescale Semiconductor