PIC18F2420-ESLASHP datasheet(55/412 Pages) MICROCHIP

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DS39631E-page 53

PIC18F2420/2520/4420/4520

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 concur-

rent 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 is

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 PIC18F2420 and PIC18F4420 each have 16 Kbytes

of Flash memory and can store up to 8,192 single-word

instructions. The PIC18F2520 and PIC18F4520 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 map for PIC18F2420/2520/

4420/4520 devices is shown in Figure 5-1.

FIGURE 5-1:

PROGRAM MEMORY MAP AND STACK FOR

PIC18F2420/2520/4420/4520 DEVICES

PC<20:0>

Stack Level 1

•

Stack Level 31

Reset Vector

Low-Priority Interrupt Vector

•

CALL,RCALL,RETURN

RETFIE,RETLW

0000h

0018h

On-Chip

Program Memory

High-Priority Interrupt Vector

0008h

1FFFFFh

4000h

3FFFh

Read ‘0’

200000h

8000h

7FFFh

On-Chip

Program Memory

Read ‘0’

PIC18F2420/4420

PIC18F2520/4520

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