PIC18F4321 datasheet(59/402 Pages) MICROCHIP

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DS39689F-page 59

PIC18F2221/2321/4221/4321 FAMILY

6.0

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 7.0

“Flash Program Memory”. Data EEPROM is

discussed separately in Section 8.0 “Data EEPROM

Memory”.

6.1

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 PIC18F2221 and PIC18F4221 each have 4 Kbytes

of Flash memory and can store up to 2048 single-word

instructions. The PIC18F2321 and PIC18F4321 each

have 8 Kbytes of Flash memory and can store up to

4096 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 PIC18F2221/4221 and

PIC18F2321/4321 devices are shown in Figure 6-1.

FIGURE 6-1:

PROGRAM MEMORY MAP AND STACK FOR PIC18F2221/2321/4221/4321 FAMILY

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

1000h

0FFFh

Read ‘0’

200000h

PC<20:0>

Stack Level 1

•

Stack Level 31

Reset Vector

Low-Priority Interrupt Vector

•

CALL,RCALL,RETURN

RETFIE,RETLW

0000h

0018h

2000h

1FFFh

On-Chip

Program Memory

High-Priority Interrupt Vector 0008h

Read ‘0’

1FFFFFh

200000h

PIC18FX221

PIC18FX321

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