AT80SND1C-ROTIL datasheet(27/210 Pages) ATMEL

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AT8xC51SND1C

4109E–8051–06/03

Dual Data Pointer

Description

The AT8xC51SND1C implement a second data pointer for speeding up code execution

and reducing code size in case of intensive usage of external memory accesses.

DPTR0 and DPTR1 are seen by the CPU as DPTR and are accessed using the SFR

addresses 83h and 84h that are the DPH and DPL addresses. The DPS bit in AUXR1

pointer 1 (see Figure 20).

Figure 20. Dual Data Pointer Implementation

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 “destina-

tion” pointer.

Below is an example of block move implementation using the 2 pointers and coded in

assembler. The latest C compiler also takes advantage of this feature by providing

enhanced algorithm libraries.

The INC instruction is a short (2 Bytes) and fast (6 CPU clocks) way to manipulate the

DPS bit in the AUXR1 register. However, note that the INC instruction does not directly

force the DPS bit to a particular state, but simply toggles it. In simple routines, such as

the block move example, only the fact that DPS is toggled in the proper sequence mat-

ters, not its actual value. In other words, the block move routine works the same whether

DPS is '0' or '1' on entry.

; ASCII block move using dual data pointers

; Modifies DPTR0, DPTR1, A and PSW

; Ends when encountering NULL character

; Note: DPS exits opposite of entry state unless an extra INC AUXR1 is added

AUXR1

EQU

0A2h

move:

mov

DPTR,#SOURCE ; address of SOURCE

inc

AUXR1

; switch data pointers

mov

DPTR,#DEST

; address of DEST

mv_loop:

inc

AUXR1

; switch data pointers

movx

A,@DPTR

; get a Byte from SOURCE

inc

DPTR

; increment SOURCE address

inc

AUXR1

; switch data pointers

movx

@DPTR,A

; write the Byte to DEST

inc

DPTR

; increment DEST address

jnz

mv_loop

; check for NULL terminator

end_move:

DPH0

DPH1

DPL0

DPS

AUXR1.0

DPH

DPL

DPL1

DPTR

DPTR0

DPTR1

AT80SND1C-ROTIL Datenblatt(PDF) 27 Page - ATMEL Corporation

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