PIC18F45K80-I Datasheet, PDF (128/622 Pages) Microchip Technology – 28/40/44/64-Pin, Enhanced Flash Microcontrollers with ECAN and nanoWatt XLP Technology

PIC18F66K80 FAMILY
6.6.3
MAPPING THE ACCESS BANK IN
INDEXED LITERAL OFFSET MODE
The use of Indexed Literal Offset Addressing mode
effectively changes how the lower part of Access RAM
(00h to 5Fh) is mapped. Rather than containing just the
contents of the bottom part of Bank 0, this mode maps
the contents from Bank 0 and a user-defined “window”
that can be located anywhere in the data memory
space.
The value of FSR2 establishes the lower boundary of
the addresses mapped into the window, while the
upper boundary is defined by FSR2 plus 95 (5Fh).
Addresses in the Access RAM above 5Fh are mapped
as previously described. (See Section 6.3.2 “Access
Bank”.) An example of Access Bank remapping in this
addressing mode is shown in Figure 6-10.
Remapping the Access Bank applies only to operations
using the Indexed Literal Offset mode. Operations that
use the BSR (Access RAM bit = 1) will continue to use
Direct Addressing as before. Any Indirect or Indexed
Addressing operation that explicitly uses any of the
indirect file operands (including FSR2) will continue to
operate as standard Indirect Addressing. Any instruc-
tion that uses the Access Bank, but includes a register
address of greater than 05Fh, will use Direct
Addressing and the normal Access Bank map.
6.6.4
BSR IN INDEXED LITERAL
OFFSET MODE
Although the Access Bank is remapped when the
extended instruction set is enabled, the operation of the
BSR remains unchanged. Direct Addressing, using the
BSR to select the data memory bank, operates in the
same manner as previously described.
FIGURE 6-10:
REMAPPING THE ACCESS BANK WITH INDEXED LITERAL
OFFSET ADDRESSING
Example Situation:
ADDWF f, d, a
FSR2H:FSR2L = 120h
Locations in the region
from the FSR2 Pointer
(120h) to the pointer plus
05Fh (17Fh) are mapped
to the bottom of the
Access RAM (000h-05Fh).
Special Function Registers
at F60h through FFFh are
mapped to 60h through
FFh, as usual.
Bank 0 addresses below
5Fh are not available in
this mode. They can still
be addressed by using the
BSR.
000h
05Fh
100h
120h
17Fh
200h
F00h
F60h
FFFh
Not Accessible
Bank 0
Window
Bank 1
Bank 2
through
Bank 14
Bank 15
SFRs
Data Memory
00h
Bank 1 “Window”
5Fh
60h
SFRs
FFh
Access Bank
DS39977F-page 128
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