Global Data Memory
4-11
Memory and I/O Spaces
4.4
Global Data Memory
Addresses in the upper 32K words (8000h–FFFFh) of local data memory can
be used for global data memory. The global memory allocation register
(GREG) determines the size of the global data-memory space, which is be-
tween 256 and 32K words. The GREG is connected to the eight LSBs of the
internal data bus and is memory-mapped to data-memory location 0005h.
Table 4–3 shows the allowable GREG values and shows the corresponding
address range set aside for global data memory. Any remaining addresses
within 8000h–FFFFh are available for local data memory.
Note:
Choose only the GREG values listed in Table 4–3. Other values lead to
fragmented memory maps.
Table 4–3. Global Data Memory Configurations
GREG Value
Local Memory
Global Memory
High Byte Low Byte
Range
Words
Range
Words
XXXX XXXX 0000 0000
0000h–FFFFh
65 536
–
0
XXXX XXXX 1000 0000
0000h–7FFFh
32 768
8000h–FFFFh
32 768
XXXX XXXX 1100 0000
0000h–BFFFh
49 152
C000h–FFFFh
16 384
XXXX XXXX 1110 0000
0000h–DFFFh
57 344
E000h–FFFFh
8 192
XXXX XXXX 1111 0000
0000h–EFFFh
61 440
F000h–FFFFh
4 096
XXXX XXXX 1111 1000
0000h–F7FFh
63 488
F800h–FFFFh
2 048
XXXX XXXX 1111 1100
0000h–FBFFh
64 512
FC00h–FFFFh
1 024
XXXX XXXX 1111 1110
0000h–FDFFh
65 024
FE00h–FFFFh
512
XXXX XXXX 1111 1111
0000h–FEFFh
65 280
FF00h–FFFFh
256
Note:
X = Don’t care
