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XC2200 Derivatives
System Units (Vol. 1 of 2)
Central Processing Unit (CPU)
User’s Manual
4-42
V2.1, 2008-08
CPUSV2_X, V2.2
4.7.2.1
Data Page Pointers DPP0, DPP1, DPP2, DPP3
These four non-bit-addressable registers select up to four different data pages to be
active simultaneously at run-time. The lower 10 bits of each DPP register select one of
the 1024 possible 16-Kbyte data pages; the upper 6 bits are reserved for future use.
The DPP registers allow access to the entire memory space in pages of 16 Kbytes each.
The DPP registers are implicitly used whenever data accesses to any memory location
are made via indirect or direct long 16-bit addressing modes (except for override
accesses via EXTended instructions and PEC data transfers). After reset, the Data Page
Pointers are initialized in such a way that all indirect or direct long 16-bit addresses result
in identical 18-bit addresses. This allows access to data pages 3 … 0 within segment 0
as shown in
. If the user does not want to use data paging, no further action
is required.
Data paging is performed by concatenating the lower 14 bits of an indirect or direct long
16-bit address with the contents of the DPP register selected by the upper two bits of the
16-bit address. The contents of the selected DPP register specify one of the 1024
possible data pages. This data page base address together with the 14-bit page offset
forms the physical 24-bit address (even if segmentation is disabled).
The selected number of segment address bits (via bitfield SALSEL) of the respective
DPP register is output on the respective segment address pins for all external data
accesses.
A DPP register can be updated via any instruction capable of modifying an SFR.
DPP0
Data Page Pointer 0
SFR (FE00
H
/00
H
)
Reset Value: 0000
H
DPP1
Data Page Pointer 1
SFR (FE02
H
/01
H
)
Reset Value: 0001
H
DPP2
Data Page Pointer 2
SFR (FE04
H
/02
H
)
Reset Value: 0002
H
DPP3
Data Page Pointer 3
SFR (FE06
H
/03
H
)
Reset Value: 0003
H
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-
-
-
-
-
-
DPPxPN
-
-
-
-
-
-
rw
Field
Bits
Type
Description
DPPxPN
[9:0]
rw
Data Page Number of DPPx
Specifies the data page selected via DPPx.