T89C51RD2-RDTIL datasheet(13/104 Pages) ATMEL

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T89C51RD2

4243G–8051–05/03

Dual Data Pointer

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 exter-

nal 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 5.) that allows the program code to switch between them

(Refer to Figure 3).

Figure 3. Use of Dual Pointer

Table 5. AUXR1: Auxiliary Register 1

External Data Memory

AUXR1(A2H)

DPS

DPH(83H) DPL(82H)

DPTR0

DPTR1

AUXR1

Address 0A2H

---

GF3

DPS

Reset value

Symbol

Function

Not implemented, reserved for future use.

(1)

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.

2. Bit 2 stuck at 0; this allows to use INC AUXR1 to toggle DPS without changing GF3.

DPS

Data Pointer Selection.

DPS

Operating Mode

0DPTR0 Selected

1DPTR1 Selected

GF3

This bit is a general purpose user flag

(2).

T89C51RD2-RDTIL Datasheet(PDF) 13 Page - ATMEL Corporation

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