PIC18F4321 Datasheet, PDF (55/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F4321 FAMILY
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 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 5-1.
FIGURE 5-1:
PROGRAM MEMORY MAP AND STACK FOR PIC18F4321 FAMILY DEVICES
PIC18FX221
PC<20:0>
CALL,RCALL,RETURN
21
RETFIE,RETLW
Stack Level 1
•
••
Stack Level 31
PIC18FX321
PC<20:0>
CALL,RCALL,RETURN
21
RETFIE,RETLW
Stack Level 1
••
•
Stack Level 31
Reset Vector
0000h
Reset Vector
0000h
High Priority Interrupt Vector 0008h
High Priority Interrupt Vector 0008h
Low Priority Interrupt Vector 0018h
Low Priority Interrupt Vector 0018h
On-Chip
Program Memory
0FFFh
1000h
On-Chip
Program Memory
1FFFh
2000h
Read ‘0’
Read ‘0’
1FFFFFh
200000h
© 2007 Microchip Technology Inc.
Preliminary
1FFFFFh
200000h
DS39689E-page 53