急！！！微机原理课本里面的汇编语言例子，用MASMPlus运行错误。请问错在哪里？

NAME EX1
PAGE 50,70
DAT SEGMENT PARA 'DAT'
A1 DB 12H,34H,56H,78H,9AH
   DB 0BCH,0DEH,0F0H
B1=$-A1
B2=B1*2
A2 DB B2 DUP(?)
DAT ENDS
STAC SEGMENT PARA STACK 'STA'
STA1 DW 100 DUP(?)
STAC ENDS
CODE SEGMENT PARA 'CODE'
     ASSUME CS:CODE,DS:DAT
     ASSUME SS:STAC,ES:DAT
STAR PROC FAR
     PUSH DS
     XOR AX,AX
     MOV AX,DAT
     MOV DS,AX
     MOV ES,AX
     LEA SI,A1
     LEA DI,A2
     MOV CX,B1
  G1:MOV BL,2
     MOV AL,[SI]
     MOV BH,AL
     PUSH CX
     MOV CL,4
     ROR AL,CL
     POP CX
  G2:AND AL,0F0H
     DAA
     ADD AL,0F0H
     ADC AL,40H
     MOV [DI],AL
     INC DI
     MOV AL,BH
     DEC BL
     JNC G2
     INC SI
     LOOP G1
     MOV SI,OFFSET A2
     MOV CX,B2
     CALL P1 
     RET
  P1 PROC
     MOV BL,2
  G: MOV DL,[SI]
     MOV AH,2
     INT 21H
     INC SI
     DEC BL
     JNZ T
     MOV DL,''
     MOV AH,2
     INT 21H
     MOV BL,2
  T: LOOP G
     RET
  P1 ENDP
     CODE ENDS
     END STAR 
运行之后有提示：fatal error A1010: unmatched block nesting : STAR

答案：修改如下：
NAME EX1
PAGE 50,70
DAT SEGMENT PARA 'DAT'
A1 DB 12H,34H,56H,78H,9AH
   DB 0BCH,0DEH,0F0H
B1=$-A1
B2=B1*2
A2 DB B2 DUP(?)
DAT ENDS
STAC SEGMENT PARA STACK 'STA'
STA1 DW 100 DUP(?)
STAC ENDS
CODE SEGMENT PARA 'CODE'
     ASSUME CS:CODE,DS:DAT
     ASSUME SS:STAC,ES:DAT
STAR PROC FAR
     PUSH DS
     XOR AX,AX
     MOV AX,DAT
     MOV DS,AX
     MOV ES,AX
     LEA SI,A1
     LEA DI,A2
     MOV CX,B1
  G1:MOV BL,2
     MOV AL,[SI]
     MOV BH,AL
     PUSH CX
     MOV CL,4
     ROR AL,CL
     POP CX
  G2:AND AL,0F0H
     DAA
     ADD AL,0F0H
     ADC AL,40H
     MOV [DI],AL
     INC DI
     MOV AL,BH
     DEC BL
     JNC G2
     INC SI
     LOOP G1
     MOV SI,OFFSET A2
     MOV CX,B2
     CALL P1 
     RET
STAR  ENDP

  P1 PROC
     MOV BL,2
  G: MOV DL,[SI]
     MOV AH,2
     INT 21H
     INC SI
     DEC BL
     JNZ T
     MOV DL,' '
     MOV AH,2
     INT 21H
     MOV BL,2
  T: LOOP G
     RET
  P1 ENDP
     CODE ENDS
     END STAR 

错误提示是消失了，但是本程序是什么功能?

其他：貌似不用改，是正确的 
=================
MOV SI,OFFSET A2
     MOV CX,B2
     CALL P1 
     RET
star endp

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