T87C5101 datasheet(11/58 Pages) ATMEL

11 / 58 page

T8xC5101/02

4233G–8051–03/03

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.

ASSEMBLY LANGUAGE

; Block move using dual data pointers

; Destroys DPTR0, DPTR1, A and PSW

; note: DPS exits opposite of entry state

; unless an extra INC AUXR1 is added

;

00A2

AUXR1 EQU 0A2H

;

0000 909000MOV DPTR,#SOURCE ; address of SOURCE

0003 05A2 INC AUXR1

; switch data pointers

0005 90A000 MOV DPTR,#DEST ; address of DEST

0008

LOOP:

0008 05A2 INC AUXR1

; switch data pointers

000A E0 MOVX A,@DPTR

; get a byte from SOURCE

000B A3 INC DPTR

; increment SOURCE address

000C 05A2 INC AUXR1

; switch data pointers

000E F0 MOVX @DPTR,A

; write the byte to DEST

000F A3 INC DPTR

; increment DEST address

0010 70F6JNZ LOOP

; check for 0 terminator

0012 05A2 INC AUXR1

; (optional) restore DPS

INC is a short (2 bytes) and fast (12 clocks) way to manipulate the DPS bit in the AUXR1

SFR. However, note that the INC instruction does not directly force the DPS bit to a par-

ticular 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 matters, not its actual value. In

other words, the block move routine works the same whether DPS is '0' or '1' on entry.

Observe that without the last instruction (INC AUXR1), the routine will exit with DPS in

the opposite state.

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