70592C Datasheet, PDF (34/314 Pages) Microchip Technology – High-Performance, 16-bit Microcontrollers

PIC24HJXXXGPX06A/X08A/X10A
4.1.1
PROGRAM MEMORY
ORGANIZATION
The program memory space is organized in word-
addressable blocks. Although it is treated as 24 bits
wide, it is more appropriate to think of each address of
the program memory as a lower and upper word, with
the upper byte of the upper word being unimplemented.
The lower word always has an even address, while the
upper word has an odd address (Figure 4-2).
Program memory addresses are always word-aligned
on the lower word, and addresses are incremented or
decremented by two during code execution. This
arrangement also provides compatibility with data
memory space addressing and makes it possible to
access data in the program memory space.
4.1.2 INTERRUPT AND TRAP VECTORS
All PIC24HJXXXGPX06A/X08A/X10A devices reserve
the addresses between 0x00000 and 0x000200 for
hard-coded program execution vectors. A hardware
Reset vector is provided to redirect code execution
from the default value of the PC on device Reset to the
actual start of code. A GOTO instruction is programmed
by the user at 0x000000, with the actual address for the
start of code at 0x000002.
PIC24HJXXXGPX06A/X08A/X10A devices also have
two interrupt vector tables, located from 0x000004 to
0x0000FF and 0x000100 to 0x0001FF. These vector
tables allow each of the many device interrupt sources
to be handled by separate Interrupt Service Routines
(ISRs). A more detailed discussion of the interrupt vec-
tor tables is provided in Section 7.1 “Interrupt Vector
Table”.
FIGURE 4-2:
PROGRAM MEMORY ORGANIZATION
msw
Address
0x000001
0x000003
0x000005
0x000007
most significant word
23
16
00000000
00000000
00000000
00000000
least significant word
8
PC Address
(lsw Address)
0
0x000000
0x000002
0x000004
0x000006
Program Memory
‘Phantom’ Byte
(read as ‘0’)
Instruction Width
DS70592C-page 34
© 2011 Microchip Technology Inc.