PIC18F258-ESLASHPQTP datasheet(39/402 Pages) MICROCHIP

39 / 402 page

DS41159E-page 37

PIC18FXX8

4.0

MEMORY ORGANIZATION

There are three memory blocks in Enhanced MCU

devices. These memory blocks are:

• Enhanced Flash Program Memory

• Data Memory

• EEPROM Data Memory

Data and program memory use separate busses,

which allows concurrent access of these blocks.

Additional detailed information on data EEPROM and

Flash program memory is provided in Section 5.0

“Data EEPROM Memory” and Section 6.0 “Flash

Program Memory”, respectively.

4.1

Program Memory Organization

The PIC18F258/458 devices have a 21-bit program

counter that is capable of addressing a 2-Mbyte

program memory space.

The Reset vector address is at 0000h and the interrupt

vector addresses are at 0008h and 0018h.

FIGURE 4-1:

PROGRAM MEMORY MAP

AND STACK FOR

PIC18F248/448

Figure 4-1 shows the diagram for program memory

map and stack for the PIC18F248 and PIC18F448.

Figure 4-2 shows the diagram for the program memory

map and stack for the PIC18F258 and PIC18F458.

4.1.1

INTERNAL PROGRAM MEMORY

OPERATION

The PIC18F258 and the PIC18F458 have 32 Kbytes of

internal Enhanced Flash program memory. This means

that the PIC18F258 and the PIC18F458 can store up to

16K of single-word instructions. The PIC18F248 and

PIC18F448 have 16 Kbytes of Enhanced Flash

program memory. This translates into 8192 single-word

instructions, which can be stored in the program

memory. Accessing a location between the physically

implemented memory and the 2-Mbyte address will

cause a read of all ‘0’s (a NOP instruction).

FIGURE 4-2:

PROGRAM MEMORY MAP

AND STACK FOR

PIC18F258/458

PC<20:0>

Stack Level 1

•

Stack Level 31

Reset Vector

Low Priority Interrupt Vector

•

0000h

0018h

On-Chip

Program Memory

High Priority Interrupt Vector 0008h

1FFFFFh

4000h

3FFFh

Read ‘0’

200000h

CALL,RCALL,RETURN

RETFIE,RETLW