Xinhai MCU flashes after pressing the start button

;After pressing the start key (PT2.1), the program realizes LED flashing
;Purpose: Learning the input and output control of I/O port
;===============================================
;Complete code download address: http://www.51hei.com/f/xhpms.rar
; filename: 111.asm
; chip : csu1181b
; author :
; date : 2012-07-18
;============================================
include csu1181b.inc
;=================================================
; program start
;==============================================
  org 0000h ;
  goto a1 ;
  org 0005h ;
;***************************************************
; Determine whether the start key is pressed
;***********************************************
a1: CLRWDT ; Clear the watchdog
  MOVLW 00H ; Store the data 00H in W for setting the I/O port as an input port
  MOVWF PT2EN ; Store the data in W in PT2EN (25h) to set the I/O port as an input port
  MOVLW 0FFH ; Store the data 0FFH in W for setting the I/O port to pull-up mode
  MOVWF PT2PU ;Store the data in W into PT2PU (26h) and set the I/O port to pull-up mode
  BTFSC PT2,1 ;Judge whether PT2.1 is 0, if yes, skip the next instruction (Judge whether a key is pressed, if yes, execute the following program, if no, wait for the key to be pressed)
  GOTO A1 ;Unconditionally transfer to A1
;***************************************************
; Flashing program segment
;***************************************************
A2: CLRWDT ;Clear watchdog
  MOVLW 0FFH ;Store the data 0FFH into W and use it to set the I/O port as output
  MOVWF PT3EN ;Store the data in W into PT3EN (29h) and set the I/O port as output
  MOVLW 0 ;Store the data 00H into W and use it to set the I/O port to disable pull-up mode
  MOVWF PT3PU ;Store the data in W in PT3PU (2ah) and set the I/O port to disable pull-up mode
  MOVLW 01010101B ;Store the data 01010101B in W and use it as the output data of the I/O port
  MOVWF PT3 ;Output the data in W from PT3 (28h) to drive external devices (light up the LED)
  CALL M001 ;Delay
  MOVLW 10101010B ;Store the data 10101010B in W and use it as the output data of the I/O port
  MOVWF PT3 ;Output the data in W from PT3 (28h) to drive external devices (light up the LED)
  CALL M001 ;Delay
  goto a2 ;Return and repeatedly execute the program
;********************************************************
; Delay program segment
;****************************************************
 
M001: MOVLW 2 ;
  MOVWF 80H ;
M002: MOVLW 248 ;
  MOVWF 81H ;
M003: MOVLW 250 ;
  MOVWF 82H ;
M004: DECFSZ 82H,1 ; (The result after decrement is stored in 82h) If the decrement is 0, skip the next instruction
; DECFSZ 82H,0 ; (The result after decrement is stored in the working register) If the decrement is 0, skip the next instruction
  GOTO M004 ;
  DECFSZ 81H,1 ;
  GOTO M003 ;
  DECFSZ 80H,1 ;
  GOTO M002 ;
  RETURN ; The subroutine returns
     to end ; End
;================================================