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        虽然现在stm32用的很多，很多国产的mcu不是很贵，但是他们和8051比较，还是有一点价格的差异。这一点，如果量不大的情况下，可能不是很在乎。但是产品量比较大的话，其实就非常可观了。所以，对于gpio/uart/pwm/ad/da/时钟中断这类简单应用，很多时候，我们都会选择8051单片机进行开发。不管是工具选择，还是使用过程，都非常方便。

1、8051编译器

        8051的编译器也是keil，一般是推荐先安装51版本的keil，再安装arm版本的keil。实在安装顺序反了，也没有关系，我们可以通过自己编写bat来编译。

https://www.keil.com/download/product/

2、自己准备编译bat文件

        如果实在ide弄不出来，其实也没关系，写一个bat也是可以自己编译的，比如这里的run.bat，

@echo off
SET PATH=%PATH%;E:\Keil_v5\C51\BIN
SET C51INC=E:\Keil_v5\C51\INC
SET C51LIB=E:\Keil_v5\C51\LIB

del *.OBJ *.hex *.lst *.m51 2>nul
C51 main.c
A51 STARTUP.A51
BL51 main.OBJ, STARTUP.OBJ TO main
OH51 main
pause

        编译过程需要STARTUP.A51，还有一个main.c。其中main.c自己写，而STARTUP.A51可以在安装的keil c51目录找一下即可。找不到的话，这里拷贝改一下名字也行，

$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 <h> Power-On Initialization of Memory
;
;  With the following EQU statements the initialization of memory
;  at processor reset can be defined:
;
; <o> IDATALEN: IDATA memory size <0x0-0x100>
;     <i> Note: The absolute start-address of IDATA memory is always 0
;     <i>       The IDATA space overlaps physically the DATA and BIT areas.
IDATALEN        EQU     80H
;
; <o> XDATASTART: XDATA memory start address <0x0-0xFFFF> 
;     <i> The absolute start address of XDATA memory
XDATASTART      EQU     0     
;
; <o> XDATALEN: XDATA memory size <0x0-0xFFFF> 
;     <i> The length of XDATA memory in bytes.
XDATALEN        EQU     0      
;
; <o> PDATASTART: PDATA memory start address <0x0-0xFFFF> 
;     <i> The absolute start address of PDATA memory
PDATASTART      EQU     0H
;
; <o> PDATALEN: PDATA memory size <0x0-0xFF> 
;     <i> The length of PDATA memory in bytes.
PDATALEN        EQU     0H
;
;</h>
;------------------------------------------------------------------------------
;
;<h> Reentrant Stack Initialization
;
;  The following EQU statements define the stack pointer for reentrant
;  functions and initialized it:
;
; <h> Stack Space for reentrant functions in the SMALL model.
;  <q> IBPSTACK: Enable SMALL model reentrant stack
;     <i> Stack space for reentrant functions in the SMALL model.
IBPSTACK        EQU     0       ; set to 1 if small reentrant is used.
;  <o> IBPSTACKTOP: End address of SMALL model stack <0x0-0xFF>
;     <i> Set the top of the stack to the highest location.
IBPSTACKTOP     EQU     0xFF +1     ; default 0FFH+1  
; </h>
;
; <h> Stack Space for reentrant functions in the LARGE model.      
;  <q> XBPSTACK: Enable LARGE model reentrant stack
;     <i> Stack space for reentrant functions in the LARGE model.
XBPSTACK        EQU     0       ; set to 1 if large reentrant is used.
;  <o> XBPSTACKTOP: End address of LARGE model stack <0x0-0xFFFF>
;     <i> Set the top of the stack to the highest location.
XBPSTACKTOP     EQU     0xFFFF +1   ; default 0FFFFH+1 
; </h>
;
; <h> Stack Space for reentrant functions in the COMPACT model.    
;  <q> PBPSTACK: Enable COMPACT model reentrant stack
;     <i> Stack space for reentrant functions in the COMPACT model.
PBPSTACK        EQU     0       ; set to 1 if compact reentrant is used.
;
;   <o> PBPSTACKTOP: End address of COMPACT model stack <0x0-0xFFFF>
;     <i> Set the top of the stack to the highest location.
PBPSTACKTOP     EQU     0xFF +1     ; default 0FFH+1  
; </h>
;</h>
;------------------------------------------------------------------------------
;
;  Memory Page for Using the Compact Model with 64 KByte xdata RAM
;  <e>Compact Model Page Definition
;
;  <i>Define the XDATA page used for PDATA variables. 
;  <i>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.
;
; <o> PPAGE number <0x0-0xFF> 
; <i> uppermost 256-byte address of the page used for PDATA variables.
PPAGE           EQU     0
;
; <o> SFR address which supplies uppermost address byte <0x0-0xFF> 
; <i> most 8051 variants use P2 as uppermost address byte
PPAGE_SFR       DATA    0A0H
;
; </e>
;------------------------------------------------------------------------------

; Standard SFR Symbols 
ACC     DATA    0E0H
B       DATA    0F0H
SP      DATA    81H
DPL     DATA    82H
DPH     DATA    83H

                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
                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
;<h> Code Banking
; <q> Select Bank 0 for L51_BANK.A51 Mode 4
#if 0   
;     <i> 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
;</h>
                LJMP    ?C_START

                END

3、准备一个main.c

        最简单的main.c就是闪灯，

// main.c - STC89C52RC LED 
#include <reg52.h>

sbit LED = P2^0;    // LED 接在 P2.0 口（低电平点亮）

void delay_ms(unsigned int ms)
{
    unsigned int i, j;
    for (i = 0; i < ms; i++)
        for (j = 0; j < 123; j++);  // 12MHz 下约 1ms
}

void main(void)
{
    while (1)
    {
        LED = 0;      
        delay_ms(100);
        
        LED = 1;      
        delay_ms(100);  
    }
}

        有了这个main.c，加上之前的STARTUP.A51，这样点击一下bat，就可以编译了。最终的话，可以看到一个hex文件。

4、写一个删除脚本

        如果出现编译错误，也会生成hex文件。这个时候可以加个pause，看下log。需要删除中间文件，就可以写一个delete.bat，

del  MAIN
del main.hex
del main.LST
del MAIN.M51
del main.OBJ
del STARTUP.LST
del STARTUP.OBJ

5、下载hex文件

        8051基本都是用串口下载，下载的软件是stc-isp。下载的板子都是8051+一个usb转串口。所以我们只需要usb连到pc上面，然后用stc-isp下载即可，本质上就是串口编程。

        下载有这么几个步骤，1）首先需要选中芯片类型，即STC89C52RC/LE52RC，这一步非常重要；2）其次选中串口；3）选择需要下载的hex文件；4）点击下载/编程；5）拨动两次单片机上面的开关，一定是拨动开关，不是reset，只有这样才能下载，不然下载不了。不出意外的话，经过这些步骤，就可以在stc-isp上面看到进度条了。

        此时找一个面包板，搭建一下环境，就可以看到led闪烁了。