PIC18LF4520ESLASHSP datasheet(74/390 Pages) MICROCHIP

74 / 390 page

PIC18F2420/2520/4420/4520

DS39631A-page 72

Preliminary

 2004 Microchip Technology Inc.

5.5.3

MAPPING THE ACCESS BANK IN

INDEXED LITERAL OFFSET 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 5-10.

Remapping of the Access Bank applies only to opera-

tions using the Indexed Literal Offset 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 5-10:

REMAPPING THE ACCESS BANK WITH INDEXED LITERAL OFFSET

ADDRESSING

Data Memory

000h

100h

200h

F80h

F00h

FFFh

Bank 1

Bank 15

Bank 2

through

Bank 14

SFRs

05Fh

ADDWF f, d, a

FSR2H:FSR2L = 120h

Locations in the region

from

the

FSR2

pointer

(120h) to the pointer plus

05Fh (17Fh) are mapped

the

bottom

the

Access RAM (000h-05Fh).

Locations in Bank 0 from

060h to 07Fh are mapped,

as usual, to the middle half

of the Access Bank.

Special File Registers 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.

Access Bank

00h

80h

FFh

7Fh

Bank 0

SFRs

Bank 1 “Window”

Bank 0

Window

Example Situation:

07Fh

120h

17Fh

5Fh

Bank 1

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