PIC18F4321 Datasheet, PDF (73/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F4321 FAMILY
5.5.3
MAPPING THE ACCESS BANK IN
INDEXED LITERAL OFFSET
ADDRESSING MODE
The use of Indexed Literal Offset Addressing mode
effectively changes how the first 96 locations of Access
RAM (00h to 5Fh) are mapped. Rather than containing
just the contents of the bottom half 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 5.3.2 “Access Bank”). An example of Access
Bank remapping in this addressing mode is shown in
Figure 5-9.
Remapping of the Access Bank applies only to opera-
tions using the Indexed Literal Offset Addressing
mode. Operations that use the BSR (Access RAM bit is
‘1’) will continue to use direct addressing as before.
5.6 PIC18 Instruction Execution and
the Extended Instruction Set
Enabling the extended instruction set adds eight
additional commands to the existing PIC18 instruction
set. These instructions are executed as described in
Section 24.2 “Extended Instruction Set”.
FIGURE 5-9:
REMAPPING THE ACCESS BANK WITH INDEXED LITERAL OFFSET
ADDRESSING MODE
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).
Locations in Bank 0, from
060h to 07Fh, are mapped
as usual to the middle of
the Access Bank.
Special Function Regis-
ters at F80h through FFFh
are mapped to 80h
through FFh, as usual.
Bank 0 addresses below
5Fh can still be addressed
by using the BSR.
000h
05Fh
07Fh
100h
120h
17Fh
200h
F00h
F80h
FFFh
Bank 0
Bank 0
Bank 1
Window
Bank 1
Bank 2
through
Bank 14
Bank 15
SFRs
Data Memory
00h
Bank 1 “Window”
5Fh
Bank 0
7Fh
80h
SFRs
FFh
Access Bank
© 2007 Microchip Technology Inc.
Preliminary
DS39689E-page 71