T89C51RD2-3CBC-L ATMEL [ATMEL Corporation], T89C51RD2-3CBC-L Datasheet - Page 13

• Manufacturer Part Number: T89C51RD2-3CBC-L
• Description: 0 to 40MHz Flash Programmable 8-bit Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

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).
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
7
AUXR1(A2H)
Address 0A2H
AUXR1
a.
b. Bit 2 stuck at 0; this allows to use INC AUXR1 to toggle DPS without changing GF3.
Symbol
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.
DPS
GF3
-
DPS
0
Function
Not implemented, reserved for future use.
Data Pointer Selection.
This bit is a general purpose user flag
Reset value
DPS
0
1
Table 3. AUXR1: Auxiliary Register 1
Operating Mode
DPTR0 Selected
DPTR1 Selected
DPH(83H) DPL(82H)
Figure 3. Use of Dual Pointer
X
-
DPTR1
X
-
DPTR0
b
.
X
a
-
X
-
GF3
0
T89C51RD2
External Data Memory
0
0
X
-
DPS
0
13