Windowing - Intel 8XC196MC User Manual

8XC196MC, MD, MH USER'S MANUAL
4.2

WINDOWING

Windowing expands the amount of memory that is accessible with register-direct addressing.
Register-direct addressing can access the lower register file with short, fast-executing instruc-
tions. With windowing, register-direct addressing can also access the upper register file and pe-
ripheral SFRs.
Windowing maps a segment of higher memory (the upper register file or peripheral SFRs) into
the lower register file. The window selection register (WSR) selects a 32-, 64-, or 128-byte seg-
ment of higher memory to be windowed into the top of the lower register file space. Figure 4-2
illustrates a 128-byte window.
128-byte Window
(WSR = 13H)
WSR Window in
Lower Register File
8XC196MC,MD
Memory-mapped SFRs must be accessed using indirect or indexed addressing
modes; they cannot be accessed through a window. Reading a memory-
mapped SFR through a window returns FFH (all ones), and writing to a
memory-mapped SFR through a window has no effect.
4-12
02FFH
01FFH
0180H
00FFH
0080H
0000H
Figure 4-2. Windowing
NOTE
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128-byte Window
(WSR = 13H)
WSR Window in
Lower Register File
8XC196MH
A3062-01