DATA SEGMENT
STR1 DB 01H,02H,05H,03H,04H
STR2 DB 5 DUP(?)
DATA ENDS

CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START:
MOV AX, DATA
MOV DS, AX
LEA SI, STR1
LEA DI, STR2+4
MOV CX, 05H

BACK: CLD
MOV AL, [SI]
MOV [DI], AL
INC SI
DEC DI
DEC CX
JNZ BACK

INT 3
CODE ENDS
END START

Output

C:\TASM>masm rev.asm
Microsoft (R) Macro Assembler Version 5.00
Copyright (C) Microsoft Corp 1981-1985, 1987.  All rights reserved.

Object filename [rev.OBJ]:
Source listing  [NUL.LST]:
Cross-reference [NUL.CRF]:

  50344 + 450312 Bytes symbol space free

      0 Warning Errors
      0 Severe  Errors

C:\TASM>link rev.obj

Microsoft (R) Overlay Linker  Version 3.60
Copyright (C) Microsoft Corp 1983-1987.  All rights reserved.

Run File [REV.EXE]:
List File [NUL.MAP]:
Libraries [.LIB]:
LINK : warning L4021: no stack segment

C:\TASM>debug rev.exe
-G

AX=0B04  BX=0000  CX=0000  DX=0000  SP=0000  BP=0000  SI=0005  DI=0004
DS=0B97  ES=0B87  SS=0B97  CS=0B98  IP=001A   NV UP EI PL ZR NA PE NC
0B98:001A CC            INT     3
-D 0B97:0000
0B97:0000  01 02 05 03 04 04 03 05-02 01 00 00 00 00 00 00   ................
0B97:0010  B8 97 0B 8E D8 8D 36 00-00 8D 3E 09 00 B9 05 00   ......6...>.....
0B97:0020  FC 8A 04 88 05 46 4F 49-75 F6 CC 2A E4 50 B8 FD   .....FOIu..*.P..
0B97:0030  05 50 FF 36 24 21 E8 77-63 83 C4 06 FF 36 24 21   .P.6$!.wc....6$!
0B97:0040  B8 0A 00 50 E8 47 5E 83-C4 04 5E 8B E5 5D C3 90   ...P.G^...^..]..
0B97:0050  55 8B EC 81 EC 84 00 C4-5E 04 26 80 7F 0A 00 74   U.......^.&....t
0B97:0060  3E 8B 46 08 8B 56 0A 89-46 FC 89 56 FE C4 5E FC   >.F..V..F..V..^.
0B97:0070  26 8A 47 0C 2A E4 40 50-8B C3 05 0C 00 52 50 E8   &.G.*[email protected].
-Q