$NOMOD51
;使编译器不使能预定义的8051符号，避免产生重复定义的错误。
;------------------------------------------------------------------------------
;This file is part of the C51 Compiler package
;Copyright (c) 1988-2002 Keil Elektronik GmbH and Keil Software, Inc.
;------------------------------------------------------------------------------
;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
;BL51 invocation:
;
;BL51 , STARTUP.OBJ
;BL51是Keil使用的链接器(Linker),这是命令行的使用格式，一般不用
;实际使用IDE环境,用project管理,有相应的按钮可以实现该功能.
;------------------------------------------------------------------------------
;
;User-defined Power-On Initialization of Memory---初始化RAM单元
;
;With the following EQU statements the initialization of memory
;at processor reset can be defined:
;
;
; the absolute start-address of IDATA memory is always 0
IDATALENEQU80H; the length of IDATA memory in bytes.--根据你选用的芯片可以适
;当的修改这些值。
;（例如所用的是52系列，该值修改为100H，即可初始化时将全部IDATA清0。如不更改，初始化时默认只清RAM的前128个字节，高128字节中的值全是0xff）
XDATASTARTEQU0H; the absolute start-address of XDATA memory--以下
;两项根据目标系统的外设配置和连接自己修改
XDATALENEQU0H; the length of XDATA memory in bytes.
PDATASTARTEQU0H; the absolute start-address of PDATA memory
PDATALENEQU0H; the length of PDATA memory in bytes.
;
;Notes:The IDATA space overlaps physically the DATA and BIT areas of the
;8051 CPU. At minimum the memory space occupied from the C51
;run-time routines must be set to zero.
;------------------------------------------------------------------------------
;
;Reentrant Stack Initilization--注意堆栈的方向：别的芯片自带的堆栈的生长方
;式是自顶向下生长的！而51的SP是自底向上的！(但51的再入堆栈也是自顶向下生长的）
;--且再入堆栈是由编译器自己管理的，一般不必去关心，只是在有再入函数的时候，根据
;函数的存储器模式使用相应的RAM空间做为再入堆栈。
;The following EQU statements define the stack pointer for reentrant
;functions and initialized it:
;Keil C默认情况不是用堆栈来传递参数的，所以造成函数不可重入，Keil要求用户显示声
;明函数是否具有可重入属性，以便为C函数调用初始化栈。
;Stack Space for reentrant functions in the SMALL model.
IBPSTACKEQU0; set to 1 if small reentrant is used.
IBPSTACKTOPEQU0FFH+1; set top of stack to highest location+1.
;
;Stack Space for reentrant functions in the LARGE model.
XBPSTACKEQU0; set to 1 if large reentrant is used.
XBPSTACKTOPEQU0FFFFH+1; set top of stack to highest location+1.
;
;Stack Space for reentrant functions in the COMPACT model.
PBPSTACKEQU0; set to 1 if compact reentrant is used.
PBPSTACKTOPEQU0FFFFH+1; set top of stack to highest location+1.
;不同内存模式下的变量位置。Keil编译器中有三种模式设置：
;Small：所有的变量都放在内部RAM区
;Compact：所有变量在默认情况下都会放在外部RAM的低256字节中(可由R0寻址)
;Large：所有变量都放在外部RAM中(DPTR寻址)
;这是由51处理器繁多的寻址模式导致的，不同的寻址模式有不同的效率
;
;------------------------------------------------------------------------------
;
;Page Definition for Using the Compact Model with 64 KByte xdata RAM
;
;The following EQU statements define the xdata page used for pdata
;variables. The EQU PPAGE must conform with the PPAGE control used
;in the linker invocation.
;
PPAGEENABLEEQU0; set to 1 if pdata object are used.
;
PPAGEEQU0; define PPAGE number.
;
PPAGE_SFRDATA0A0H; SFR that supplies uppermost address byte
;(most 8051 variants use P2 as uppermost address byte)很多的外部页面寻址以P2
;口为高位地址的数值，有使
