AT80C54_14 Datasheet, PDF (13/62 Pages) ATMEL Corporation – 8051 pin and instruction compatible

AT/TS8xC54/8X2
7.1 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
; 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 909000
MOV DPTR,#SOURCE
0003 05A2
INC AUXR1
0005 90A000
MOV DPTR,#DEST
0008
LOOP:
0008 05A2
INC AUXR1
000A E0
MOVX A,@DPTR
000B A3
INC DPTR
000C 05A2
INC AUXR1
000E F0
MOVX @DPTR,A
000F A3
INC DPTR
0010 70F6
JNZ LOOP
0012 05A2
INC AUXR1
; address of SOURCE
; switch data pointers
; address of DEST
; switch data pointers
; get a byte from SOURCE
; increment SOURCE address
; switch data pointers
; write the byte to DEST
; increment DEST address
; check for 0 terminator
; (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 instruc-
tion (INC AUXR1), the routine will exit with DPS in the opposite state.
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