PIC18F2455_07 Datasheet, PDF (59/430 Pages) Microchip Technology – 28/40/44-Pin, High Performance, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2455/2550/4455/4550
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 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 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 PIC18F2455 and PIC18F4455 each have
24 Kbytes of Flash memory and can store up to 12,288
single-word instructions. The PIC18F2550 and
PIC18F4550 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 maps for PIC18FX455 and
PIC18FX550 devices are shown in Figure 5-1.
FIGURE 5-1:
PROGRAM MEMORY MAP AND STACK FOR PIC18F2455/2550/4455/4550 DEVICES
PIC18FX455
PC<20:0>
CALL, RCALL, RETURN,
21
RETFIE, RETLW, CALLW,
ADDULNK, SUBULNK
Stack Level 1
•
••
Stack Level 31
Reset Vector
0000h
High Priority Interrupt Vector 0008h
Low Priority Interrupt Vector 0018h
PIC18FX550
PC<20:0>
CALL, RCALL, RETURN,
21
RETFIE, RETLW, CALLW,
ADDULNK, SUBULNK
Stack Level 1
••
•
Stack Level 31
Reset Vector
0000h
High Priority Interrupt Vector 0008h
Low Priority Interrupt Vector 0018h
On-Chip
Program Memory
5FFFh
6000h
On-Chip
Program Memory
7FFFh
8000h
Read ‘0’
Read ‘0’
1FFFFFh
200000h
© 2007 Microchip Technology Inc.
Preliminary
1FFFFFh
200000h
DS39632D-page 57