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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