PIC24FJ64GA705 Datasheet, PDF (57/412 Pages) –

PIC24FJ256GA705 FAMILY
TABLE 4-13: EDS MEMORY ADDRESS WITH DIFFERENT PAGES AND ADDRESSES
DSRPAG
(Data Space Read
Register)
DSWPAG
(Data Space Write
Register)
Source/Destination
Address while
Indirect
Addressing
24-Bit EA
Pointing to EDS
Comment
x⁽¹⁾
x⁽¹⁾
0000h to 1FFFh
000000h to
Near Data Space⁽²⁾
001FFFh
2000h to 7FFFh
002000h to
007FFFh
001h
001h
008000h to
00FFFEh
002h
002h
010000h to
017FFEh
003h
•
•
•
•
•
1FFh
003h
•
•
•
•
•
1FFh
8000h to FFFFh
018000h to
0187FEh
•
•
•
•
FF8000h to
FFFFFEh
EPMP Memory Space
000h
000h
Invalid Address Address Error Trap⁽³⁾
Note 1:
2:
3:
If the source/destination address is below 8000h, the DSRPAG and DSWPAG registers are not considered.
This Data Space can also be accessed by Direct Addressing.
When the source/destination address is above 8000h and DSRPAG/DSWPAG are ‘0’, an address error
trap will occur.
4.2.6 SOFTWARE STACK
Apart from its use as a Working register, the W15
register in PIC24F devices is also used as a Software
Stack Pointer (SSP). The pointer always points to the
first available free word and grows from lower to higher
addresses. It pre-decrements for stack pops and post-
increments for stack pushes, as shown in Figure 4-6.
Note that for a PC push during any CALL instruction,
the MSB of the PC is zero-extended before the push,
ensuring that the MSB is always clear.
Note:
A PC push during exception processing
will concatenate the SRL register to the
MSB of the PC prior to the push.
The Stack Pointer Limit Value register (SPLIM), associ-
ated with the Stack Pointer, sets an upper address
boundary for the stack. SPLIM is uninitialized at Reset.
As is the case for the Stack Pointer, SPLIM<0> is
forced to ‘0’ as all stack operations must be word-
aligned. Whenever an EA is generated using W15 as a
source or destination pointer, the resulting address is
compared with the value in SPLIM. If the contents of
the Stack Pointer (W15) and the SPLIM register are
equal, and a push operation is performed, a stack error
trap will not occur. The stack error trap will occur on a
subsequent push operation. Thus, for example, if it is
desirable to cause a stack error trap when the stack
grows beyond address 2000h in RAM, initialize the
SPLIM with the value, 1FFEh.
Similarly, a Stack Pointer underflow (stack error) trap is
generated when the Stack Pointer address is found to
be less than 0800h. This prevents the stack from
interfering with the SFR space.
A write to the SPLIM register should not be immediately
followed by an indirect read operation using W15.
FIGURE 4-6:
0000h ₁₅
CALL STACK FRAME
0
PC<15:0>
000000000 PC<22:16>
<Free Word>
W15 (before CALL)
W15 (after CALL)
POP : [--W15]
PUSH : [W15++]
 2016 Microchip Technology Inc.
DS30010118B-page 57