Datasheet

© 2007 Microchip Technology Inc. DS39629C-page 65
PIC18F6390/6490/8390/8490
5.0 MEMORY ORGANIZATION
There are two types of memory in PIC18 Flash
microcontroller devices:
• Program Memory
• Data RAM
As Harvard architecture devices, the data and program
memories use separate busses; this allows for
concurrent access of the two memory spaces.
Additional detailed information on the operation of the
Flash program memory is provided in Section 6.0
“Flash Program 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 PIC18FX390 have 8 Kbytes of Flash memory and
can store up to 4,096 single-word instructions and the
PIC18FX490 have 16 Kbytes of Flash memory and can
store up to 8,192 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
PIC18F6390/6490/8390/8490 devices are shown in
Figure 5-1.
FIGURE 5-1: PROGRAM MEMORY MAP AND STACK FOR PIC18F6390/6490/8390/8490 DEVICES
PC<20:0>
Stack Level 1
•
Stack Level 31
Reset Vector
Low-Priority Interrupt Vector
•
•
CALL,RCALL,RETURN
RETFIE,RETLW
21
0000h
0018h
On-Chip
Program Memory
High-Priority Interrupt Vector
0008h
User Memory Space
1FFFFFh
2000h
1FFFh
Read ‘0’
PC<20:0>
Stack Level 1
•
Stack Level 31
Reset Vector
Low-Priority Interrupt Vector
•
•
CALL,RCALL,RETURN
RETFIE,RETLW
21
0000h
0018h
On-Chip
Program Memory
High-Priority Interrupt Vector
0008h
User Memory Space
1FFFFFh
4000h
3FFFh
Read ‘0’
PIC18F6390/8390 PIC18F6490/8490