XC886/888CLM
Memory Organization
User’s Manual
3-4
V1.3, 2010-02
Memory Organization, V 1.2
D-Flash banks need to be used for program code based on address spaces 6000
H
–
6FFF
H
and 7000
H
– 7FFB
H
. This allows program code developed using the Flash device
to be migrated to the ROM device without any changes.
In the case that only 28 Kbytes of program code (later stored in 32-Kbyte ROM memory)
is required for the ROM device with the available D-Flash bank (in the ROM device) used
for data, then D-Flash Bank 1 in the Flash device should be used for program code
development based on address space 6000
H
– 6FFF
H
while D-Flash Bank 0 is used for
data based on address space A000
H
– AFFF
H
. This way, migration of program code
from the Flash to ROM device can be performed without any changes.
3.2
Program Memory
The performance of the CPU is optimized with a dedicated interface for direct interfacing
with the program memory without using any port pin. This means that a code fetch can
occur on every rising edge of the clock. Hence, there is no concept of ‘internal’ or
‘external’ program memory as all code is fetched from a single program memory
interface.
3.3
Data Memory
The data memory space consists of an internal and external memory space. The labels
‘internal’ and ‘external’ for data memory are used to distinguish between the register
memory and the 64-Kbyte data space accessed using ‘MOVX’ instructions. They do not
imply that the external data memory is located off-chip.
3.3.1
Internal Data Memory
The internal data memory is divided into two physically separate and distinct blocks: the
256-byte RAM and the 128-byte Special Function Register (SFR) area. While the upper
128 bytes of RAM and the SFR area share the same address locations, they are
accessed through different addressing modes. The lower 128 bytes of RAM can be
accessed through either direct or register indirect addressing, while the upper 128 bytes
of RAM can be accessed through register indirect addressing only. The SFRs are
accessible through direct addressing.
The 16 bytes of RAM that occupy addresses from 20
H
to 2F
H
are bitaddressable. RAM
occupying direct addresses from 30
H
to 7F
H
can be used as scratch pad registers or
used for the stack.
*
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