PIC18F4550ESOSQTP datasheet(59/430 Pages) MICROCHIP

59 / 430 page

Preliminary

DS39632D-page 57

PIC18F2455/2550/4455/4550

5.0

MEMORY ORGANIZATION

There are three types of memory in PIC18 enhanced

microcontroller devices:

• Program Memory

• Data RAM

• Data EEPROM

As Harvard architecture devices, the data and program

memories use separate busses; this allows for con-

current access of the two memory spaces. The data

EEPROM, for practical purposes, can be regarded as

a peripheral device, since it is addressed and accessed

through a set of control registers.

Additional detailed information on the operation of the

Flash program memory is provided in Section 6.0

“Flash

Program

Memory”.

Data

EEPROM

discussed separately in Section 7.0 “Data EEPROM

Memory”.

5.1

Program Memory Organization

PIC18 microcontrollers implement a 21-bit program

counter which is capable of addressing a 2-Mbyte

program memory space. Accessing a location between

the upper boundary of the physically implemented

memory and the 2-Mbyte address will return all ‘0’s (a

NOP

instruction).

The

PIC18F2455

and

PIC18F4455

each

have

24 Kbytes of Flash memory and can store up to 12,288

single-word

instructions.

The

PIC18F2550

and

PIC18F4550 each have 32 Kbytes of Flash memory

and can store up to 16,384 single-word instructions.

PIC18 devices have two interrupt vectors. The Reset

vector address is at 0000h and the interrupt vector

addresses are at 0008h and 0018h.

The program memory maps for PIC18FX455 and

PIC18FX550 devices are shown in Figure 5-1.

FIGURE 5-1:

PROGRAM MEMORY MAP AND STACK FOR PIC18F2455/2550/4455/4550 DEVICES

PC<20:0>

Stack Level 1

•

Stack Level 31

Reset Vector

Low Priority Interrupt Vector

•

CALL, RCALL, RETURN,

RETFIE, RETLW, CALLW,

0000h

0018h

On-Chip

Program Memory

High Priority Interrupt Vector 0008h

1FFFFFh

6000h

5FFFh

Read ‘0’

200000h

PC<20:0>

Stack Level 1

•

Stack Level 31

Reset Vector

Low Priority Interrupt Vector

•

CALL, RCALL, RETURN,

RETFIE, RETLW, CALLW,

0000h

0018h

8000h

7FFFh

On-Chip

Program Memory

High Priority Interrupt Vector 0008h

Read ‘0’

1FFFFFh

200000h

PIC18FX455

PIC18FX550

ADDULNK, SUBULNK

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