Datasheet

PIC18F2450/4450
© 2008 Microchip Technology Inc. DS39760D-page 53
5.0 MEMORY ORGANIZATION
There are two types of memory in PIC18F2450/4450
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 PIC18F2450 and PIC18F4450 each have 16 Kbytes
of Flash memory and can store up to 8192 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 PIC18F2450 and
PIC18F4450 devices are shown in Figure 5-1.
FIGURE 5-1: PROGRAM MEMORY MAP AND STACK FOR PIC18F2450/4450 DEVICES
PC<20:0>
Stack Level 1
•
Stack Level 31
Reset Vector
Low-Priority Interrupt Vector
•
•
CALL, RCALL, RETURN,
RETFIE, RETLW, CALLW,
21
0000h
0018h
On-Chip
Program Memory
High-Priority Interrupt Vector
0008h
User Memory Space
1FFFFFh
4000h
3FFFh
Read ‘0’
200000h
PIC18F2450/4450
ADDULNK, SUBULNK