这几天在做C8051F340的一个程序，用到USB，我在修改了他的Demo，加了一些数据在xdata里，程序编译通过，无错误无警告，但在仿真的时候一直进不了main函数，我发现很多人遇到了和我一样的问题，在网络上搜索了很长时间，才发现解决之道，现在贴出来共享：
修改STARTUP.A51函数，在启动代码中关闭看门狗如下：
$NOMOD51
;------------------------------------------------------------------------------
; This file is part of the C51 Compiler package
; Copyright (c) 1988-2005 Keil Elektronik GmbH and Keil Software, Inc.
; Version 8.01
;
; *** <<< Use Configuration Wizard in Context Menu >>> ***
;------------------------------------------------------------------------------
; STARTUP.A51: This code is executed after processor reset.
;
; To translate this file use A51 with the following invocation:
;
; A51 STARTUP.A51
;
; To link the modified STARTUP.OBJ file to your application use the following
; Lx51 invocation:
;
; Lx51 your object file list, STARTUP.OBJ controls
;
;------------------------------------------------------------------------------
;
; User-defined
;
; With the following EQU statements the initialization of memory
; at processor reset can be defined:
;
;
; Note: The absolute start-address of IDATA memory is always 0
; The IDATA space overlaps physically the DATA and BIT areas.
IDATALEN EQU 80H
;
;
; The absolute start address of XDATA memory
XDATASTART EQU 0
;
;
; The length of XDATA memory in bytes.
XDATALEN EQU 0
;
;
; The absolute start address of PDATA memory
PDATASTART EQU 0H
;
;
; The length of PDATA memory in bytes.
PDATALEN EQU 0H
;
;
;------------------------------------------------------------------------------
;
;
;
; The following EQU statements define the stack pointer for reentrant
; functions and initialized it:
;
;
; IBPSTACK: Enable SMALL model reentrant stack
; Stack space for reentrant functions in the SMALL model.
IBPSTACK EQU 0 ; set to 1 if small reentrant is used.
;
; Set the top of the stack to the highest location.
IBPSTACKTOP EQU 0xFF +1 ; default 0FFH+1
;
;
;
; XBPSTACK: Enable LARGE model reentrant stack
; Stack space for reentrant functions in the LARGE model.
XBPSTACK EQU 0 ; set to 1 if large reentrant is used.
;
; Set the top of the stack to the highest location.
XBPSTACKTOP EQU 0xFFFF +1 ; default 0FFFFH+1
;
;
;
; PBPSTACK: Enable COMPACT model reentrant stack
; Stack space for reentrant functions in the COMPACT model.
PBPSTACK EQU 0 ; set to 1 if compact reentrant is used.
;
;
; Set the top of the stack to the highest location.
PBPSTACKTOP EQU 0xFF +1 ; default 0FFH+1
;
;
;------------------------------------------------------------------------------
;
; Memory Page for Using the Compact Model with 64 KByte xdata RAM
;
;
; Define the XDATA page used for PDATA variables.
; PPAGE must conform with the PPAGE set in the linker invocation.
;
; Enable pdata memory page initalization
PPAGEENABLE EQU 0 ; set to 1 if pdata object are used.
;
;
; uppermost 256-byte address of the page used for PDATA variables.
PPAGE EQU 0
;
;
; most 8051 variants use P2 as uppermost address byte
PPAGE_SFR DATA 0A0H
;
;
;------------------------------------------------------------------------------
; Standard SFR Symbols
ACC DATA 0E0H
B DATA 0F0H
SP DATA 81H
DPL DATA 82H
DPH DATA 83H
PCA0MD DATA 0D9H //Added by auzxj，2009年6月22日
NAME ?C_STARTUP
?C_C51STARTUP SEGMENT CODE
?STACK SEGMENT IDATA
RSEG ?STACK
DS 1
EXTRN CODE (?C_START)
PUBLIC ?C_STARTUP
CSEG AT 0
?C_STARTUP: LJMP STARTUP1
RSEG ?C_C51STARTUP
STARTUP1:
IF IDATALEN <> 0
ANL PCA0MD, #NOT(040h)//Added by auzxj，2009年6月22日
MOV R0,#IDATALEN - 1
CLR A
IDATALOOP: MOV @R0,A
DJNZ R0,IDATALOOP
ENDIF
IF XDATALEN <> 0
MOV DPTR,#XDATASTART
MOV R7,#LOW (XDATALEN)
IF (LOW (XDATALEN)) <> 0
MOV R6,#(HIGH (XDATALEN)) +1
ELSE
MOV R6,#HIGH (XDATALEN)
ENDIF
CLR A
XDATALOOP: MOVX @DPTR,A
INC DPTR
DJNZ R7,XDATALOOP
DJNZ R6,XDATALOOP
ENDIF
IF PPAGEENABLE <> 0
MOV PPAGE_SFR,#PPAGE
ENDIF
IF PDATALEN <> 0
MOV R0,#LOW (PDATASTART)
MOV R7,#LOW (PDATALEN)
CLR A
PDATALOOP: MOVX @R0,A
INC R0
DJNZ R7,PDATALOOP
ENDIF
IF IBPSTACK <> 0
EXTRN DATA (?C_IBP)
MOV ?C_IBP,#LOW IBPSTACKTOP
ENDIF
IF XBPSTACK <> 0
EXTRN DATA (?C_XBP)
MOV ?C_XBP,#HIGH XBPSTACKTOP
MOV ?C_XBP+1,#LOW XBPSTACKTOP
ENDIF
IF PBPSTACK <> 0
EXTRN DATA (?C_PBP)
MOV ?C_PBP,#LOW PBPSTACKTOP
ENDIF
MOV SP,#?STACK-1
; This code is required if you use L51_BANK.A51 with Banking Mode 4
;
; Select Bank 0 for L51_BANK.A51 Mode 4
#if 0
; Initialize bank mechanism to code bank 0 when using L51_BANK.A51 with Banking Mode 4.
EXTRN CODE (?B_SWITCH0)
CALL ?B_SWITCH0 ; init bank mechanism to code bank 0
#endif
;
LJMP ?C_START
END
修改保存，并把它添加进你的工程
====
---------------------------------------------------------------------------------------------
修改init.a51文件也可以，里面其实有介绍。
; User-defined Watch-Dog Refresh.
;
; If the C application contains many initialized variables uses a watchdog
; it might be possible that the user has to include a watchdog refresh into
; the initialization process. The watchdog refresh routine can be included
; in the following MACRO and can alter all CPU registers except
; DPTR.
;
WATCHDOG MACRO
; Include any Watchdog refresh code here
ENDM
;