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T89C51RD2-DDFC-L View Datasheet(PDF) - Atmel Corporation

Part Name
Description
Manufacturer
T89C51RD2-DDFC-L
Atmel
Atmel Corporation Atmel
T89C51RD2-DDFC-L Datasheet PDF : 86 Pages
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T89C51RD2
6.2. Dual Data Pointer Register Ddptr
The additional data pointer can be used to speed up code execution and reduce code size.
The dual DPTR structure is a way by which the chip will specify the address of an external data memory location.
There are two 16-bit DPTR registers that address the external memory, and a single bit called
DPS = AUXR1/bit0 (See Table 3.) that allows the program code to switch between them (Refer to Figure 3).
External Data Memory
7
0
DPS
AUXR1(A2H)
DPTR1
DPTR0
DPH(83H) DPL(82H)
Figure 3. Use of Dual Pointer
AUXR1
Address 0A2H
Table 3. AUXR1: Auxiliary Register 1
Reset value
-
-
-
-
GF3
0
X
X
X
X
0
0
Symbol
-
DPS
GF3
Function
Not implemented, reserved for future use.a
Data Pointer Selection.
DPS
Operating Mode
0
DPTR0 Selected
1
DPTR1 Selected
This bit is a general purpose user flagb.
-
DPS
X
0
a. User software should not write 1s to reserved bits. These bits may be used in future 8051 family
products to invoke new feature. In that case, the reset value of the new bit will be 0, and its active
value will be 1. The value read from a reserved bit is indeterminate.
b. Bit 2 stuck at 0; this allows to use INC AUXR1 to toggle DPS without changing GF3.
Application
Software can take advantage of the additional data pointers to both increase speed and reduce code size, for
example, block operations (copy, compare, search ...) are well served by using one data pointer as a ’source’
pointer and the other one as a "destination" pointer.
ASSEMBLY LANGUAGE
Rev. F - 15 February, 2001
13
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