PIC18F1230-ESLASHMLQTP datasheet(65/312 Pages) MICROCHIP

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PIC18F1230/1330

Advance Information

DS39758B-page 63

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

operations 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 21.2 “Extended Instruction Set”.

FIGURE 5-9:

REMAPPING THE ACCESS BANK WITH INDEXED LITERAL OFFSET

ADDRESSING MODE

Data Memory

000h

100h

F80h

F00h

FFFh

Bank 0

Bank 15

Bank 1

through

Bank 14

SFRs

05Fh

ADDWF f, d, a

FSR2H:FSR2L = 090h

Locations in the region

from the FSR2 Pointer

(090h) to the pointer plus

05Fh (0EFh) are mapped

the

bottom

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 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

SFRs

Bank 0 “Window”

Bank 0

Window

Example Situation:

07Fh

090h

0EFh

5Fh

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