Rainbow Electronics T89C51RD2 User Manual
Page 14
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Rev. F - 15 February, 2001
T89C51RD2
; Block move using dual data pointers
; Modifies 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 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 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.