PIC18LF4331-ESLASHML datasheet(67/392 Pages) MICROCHIP

67 / 392 page

 2010 Microchip Technology Inc.

DS39616D-page 67

PIC18F2331/2431/4331/4431

6.5

Data Memory Organization

The data memory in PIC18 devices is implemented as

static RAM. Each register in the data memory has a 12-bit

address, allowing up to 4,096 bytes of data memory. The

memory space is divided into as many as 16 banks that

contain 256 bytes each. PIC18F2331/2431/4331/4431

devices implement all 16 banks.

Figure 6-6 shows the data memory organization for the

PIC18F2331/2431/4331/4431 devices. The data mem-

ory contains Special Function Registers (SFRs) and

General Purpose Registers (GPRs). The SFRs are used

for control and status of the controller and peripheral

functions, while GPRs are used for data storage and

scratchpad operations in the user’s application. Any

read of an unimplemented location will read as ‘0’s.

The instruction set and architecture allow operations

across all banks. The entire data memory may be

accessed by Direct, Indirect or Indexed Addressing

modes. Addressing modes are discussed later in this

subsection.

To ensure that commonly used registers (SFRs and

select GPRs) can be accessed in a single cycle, PIC18

devices implement an Access Bank. This is a 256-byte

memory space that provides fast access to SFRs and

the lower portion of GPR Bank 0 without using the

BSR. Section 6.5.2 “Access Bank” provides a

detailed description of the Access RAM.

FIGURE 6-6:

DATA MEMORY MAP FOR PIC18F2331/2431/4331/4431 DEVICES

Bank 0

Bank 1

Bank 14

Bank 15

Data Memory Map

BSR<3:0>

= 0000

= 0001

= 1111

060h

05Fh

F60h

FFFh

00h

5Fh

60h

FFh

Access Bank

When a = 0:

The BSR is ignored and the

Access Bank is used.

The first 96 bytes are

General Purpose RAM

(from Bank 0).

The second 160 bytes are

Special Function Registers

(from Bank 15).

When a = 1:

The BSR specifies the bank

used by the instruction.

F5Fh

F00h

EFFh

1FFh

100h

0FFh

000h

Access RAM

FFh

00h

FFh

00h

FFh

00h

GPR

SFR

Unused

Access RAM High

Access RAM Low

Bank 3

200h

Unused

Read ‘00h’

= 1110

= 0011

(SFRs)

= 0010

GPR

FFh

00h

Bank 2

300h

2FFh

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