⑴ 单片机上写的串口程序是什么意思啊
单片机（MCU）也就是人们所说的微处理器。可以理解为应用于嵌入式或工业控制上的小型CPU。与我们PC中CPU不同的是，单片机是一个处理器核与一些人们常用到的硬件资源封装到一片芯片里了。
例如你这里说到的串口，它是工控中最常使用到的通信方式之一，几乎所有的MCU内都会集成串口资源。而PC中串口一般是在主板上外扩一片16C554芯片扩屏出来的。当然在需要多串口的场合，MCU也可以通过控制16C55x来扩屏出串口。
你提到的TMOD，SCON，SBUF是C51/52系列单片机中的与串口控制相关的寄存器。
为了简单说明，给你一段程序，我加上注释给你：
void InitComm() //初始化C51单片机串口
{//设置定时器1为波特率发生器
PCON |= 0x80; //设置波特率加倍
TMOD |= 0x20; //设置定时器1为方式2运行
TH1 = (unsigned char)(0xXXXX); //设置定时常数。一般0xXXXX由系统晶振与通信目标波特率所定.
TR1 = 1; //启动定时器1
SCON = 0x50; //串行口方式1，允许串行接收。
ES = 1; //允许串口中断
}
//串行中断服务程序
void it_comm(void ) interrupt 4 using 1
{
if (RI)
{//接收数据中断
RI = 0;
}
if (TI)
{//发送数据中断
TI = 0;
}
}
////////////////////////
补充：
RS232协议是串口通信协议，它是由硬件自动完成的。也就是说，像开始位，停止位，效验等等，都是由硬件自动加上去的。对于程序员来讲，可以认为是透明的。只需要初始化时定义好就可以了。
你提到的MAX232只是做电平转换用的。和RS232协议没有直接关系。
⑵ 我用mplab 编写一个pic18f252的c 程序,创建时显示:can't open "pic.h" head file such director
搜索栏里找PIC.H
你看看是这个不:
#ifndef _PIC_H
#define _PIC_H
#if defined(_10F200) || defined(_10F202) ||\\
defined(_10F204) || defined(_10F206)
#include <pic10f20x.h>
#endif
#if defined(_12C508) || defined(_12C509) ||\\
defined(_12F508) || defined(_12F509) ||\\
defined(_12C508A) || defined(_12C509A) ||\\
defined(_12CE518) || defined(_12CE519) ||\\
defined(_12C509AG) || defined(_12C509AF) ||\\
defined(_12CR509A) || defined(_RF509AG) ||\\
defined(_RF509AF)
#include <pic125xx.h>
#endif
#if defined(_16C432) || defined(_16C433)
#include <43x.h>
#endif
#if defined(_16C52) || defined(_16C54) || defined(_16C54A) ||\\
defined(_16C54B) || defined(_16C54C) || defined(_16CR54A) ||\\
defined(_16CR54B) || defined(_16CR54C) || defined(_16C55) ||\\
defined(_16C55A) || defined(_16C56) || defined(_16C56A) ||\\
defined(_16CR56A) || defined(_16C57) || defined(_16C57C) ||\\
defined(_16CR57B) || defined(_16CR57C) || defined(_16C58A) ||\\
defined(_16C58B) || defined(_16CR58A) || defined(_16CR58B) ||\\
defined(_16C58) || defined(_16HV540)
#include <5x.h>
#endif
#if defined(_16F54) || defined(_16F57)
#include <f5x.h>
#endif
#if defined(_12C671) || defined(_12C672) ||\\
defined(_12CE673) || defined(_12CE674)
#include <pic1267x.h>
#endif
#if defined(_12F629) || defined(_12F675)
#include <pic12f6x.h>
#endif
#if defined(_12F683)
#include <pic12f683.h>
#endif
#if defined(_12F675F) || defined(_12F675H) || defined(_12F675K)
#include <pic12rf675.h>
#endif
#if defined(_16C505) || defined(_16F505)
#include <505.h>
#endif
#ifdef _14000
#include <pic14000.h>
#endif
#if defined(_16C554) || defined(_16C556) || defined(_16C557) || \\
defined(_16C558) || defined(_16C554A) || defined(_16C556A) || \\
defined(_16C558A)
#include <55x.h>
#endif
#ifdef _16C61
#include <61.h>
#endif
#if defined(_16C62) || defined(_16C62A) || defined(_16CR62) ||\\
defined(_16C62B)
#include <62.h>
#endif
#if defined(_16C620) || defined(_16C621) || defined(_16C622) ||\\
defined(_16C620A) || defined(_16C621A) || defined(_16C622A) ||\\
defined(_16CE623) || defined(_16CE624) || defined(_16CE625) ||\\
defined(_16CR620A)
#include <62x.h>
#endif
#if defined(_16C64) || defined(_16C64A) || defined(_16CR64)
#include <64.h>
#endif
#if defined(_16C641) || defined(_16C642) ||\\
defined(_16C661) || defined(_16C662)
#include <6xx.h>
#endif
#if defined(_16C65) || defined(_16C65A) || defined(_16CR65)
#include <65.h>
#endif
#if defined(_16C66) || defined(_16C67)
#include <6x.h>
#endif
#if defined(_16C71) || defined(_16C710) || defined(_16C711)
#include <71x.h>
#endif
#if defined(_16C712) || defined(_16C715) || defined(_16C716)
#include <715.h>
#endif
#if defined(_16C72) || defined(_16C72A) || defined(_16CR72)
#include <72.h>
#endif
#if defined(_16C73) || defined(_16C73A) ||\\
defined(_16C74) || defined(_16C74A) ||\\
defined(_16C63) || defined(_16CR63) || defined(_16C63A) ||\\
defined(_16C65B) || defined(_16C73B) || defined(_16C74B) ||\\
defined(_16LC74B)
#include <74.h>
#endif
#if defined(_16C76) || defined(_16C77)
#include <77.h>
#endif
#if defined(_16C773) || defined(_16C774) || defined(_16C770) ||\\
defined(_16C771) || defined(_16C717) || defined(_16C745) ||\\
defined(_16C765)
#include <77x.h>
#endif
#if defined(_16C781) || defined(_16C782)
#include <78x.h>
#endif
#if defined(_16F627) || defined(_16F628)
#include <f6x.h>
#endif
#if defined(_16F627A) || defined(_16F628A) || defined(_16F648A)
#include <f62xa.h>
#endif
#if defined(_16F630) || defined(_16F676)
#include <630.h>
#endif
#if defined(_12F635) || defined(_16F636)
#include <f636.h>
#endif
#if defined(_16F684)
#include <f684.h>
#endif
#if defined(_16F688)
#include <f688.h>
#endif
#if defined(_16F83) || defined(_16CR83) || defined(_16C84) || \\
defined(_16F84) || defined(_16F84A) || defined(_16CR84)
#include <84.h>
#endif
#if defined(_16F87) || defined(_16F88)
#include <f87.h>
#endif
#if defined(_16F873) || defined(_16F874) ||\\
defined(_16F876) || defined(_16F877) ||\\
defined(_16F872) || defined(_16F871) ||\\
defined(_16F870)
#include <87x.h>
#endif
#if defined(_16F873A) || defined(_16F874A) ||\\
defined(_16F876A) || defined(_16F877A)
#include <8xa.h>
#endif
#if defined(_16F72) ||\\
defined(_16F73) || defined(_16F74) ||\\
defined(_16F76) || defined(_16F77)
#include <f7x.h>
#endif
#if defined(_16F716)
#include <f716.h>
#endif
#if defined(_16F737) || defined(_16F747) ||\\
defined(_16F767) || defined(_16F777)
#include <f7x7.h>
#endif
#if defined(_16F818) || defined(_16F819)
#include <f81x.h>
#endif
#if defined(_16C923) || defined(_16C924) ||\\
defined(_16C925) || defined(_16C926)
#include <9xx.h>
#endif
#if defined(_7C695X)
#include <pic7695x.h>
#endif
#if defined(_16C99) || defined (_16C99C)
#include <99.h>
#endif
#if defined(_17C42) || defined(_17C42A) || defined(_17CR42) ||\\
defined(_17C43) || defined(_17CR43) || defined(_17C44)
#include <pic174x.h>
#endif
#if defined(_17C752) || defined(_17C756) || defined(_17C756A) ||\\
defined(_17C762) || defined(_17C766)
#include <pic177xx.h>
#endif
#define CLRWDT() asm("clrwdt")
#define SLEEP() asm("sleep")
#define NOP() asm("nop")
#define ___mkstr1(x) #x
#define ___mkstr(x) ___mkstr1(x)
#define __CONFIG(x) asm("\\tpsect config,class=CONFIG,delta=2");\\
asm("\\tdw "___mkstr(x))
#define __IDLOC(w) asm("\\tpsect idloc,class=IDLOC,delta=2");\\
asm("\\tglobal\\tidloc_word"); \\
asm("idloc_word"); \\
asm("\\tirpc\\t__arg," ___mkstr(w)); \\
asm("\\tdw 0&__arg&h"); \\
asm("\\tendm")
#if EEPROM_SIZE > 0
#define __EEPROM_DATA(a, b, c, d, e, f, g, h) \\
asm("\\tpsect eeprom_data,class=EEDATA,delta=2"); \\
asm("\\tdb\\t" ___mkstr(a) "," ___mkstr(b) "," ___mkstr(c) "," ___mkstr(d) "," \\
___mkstr(e) "," ___mkstr(f) "," ___mkstr(g) "," ___mkstr(h))
#endif
/***********************************************************************
**** FLASH memory read/write/erase macros and function definitions ****
***********************************************************************
* Notes:
* __FLASHTYPE == 0 defined in devices that can only read flash memory - cannot write eg. 16F777
* __FLASHTYPE == 1 defined in traditional devices that can write 1 word at a time eg. 16F877
* __FLASHTYPE == 2 defined in devices that can only write in 4 word blocks eg. 16F877A
* __FLASHTYPE == 3 defined in devices requiring 32-word block erasure before writing eg. 16F87
* __FLASHTYPE == undefined if device can neither read nor write program memory
*/
// macro FLASH_READ returns a word stored at a flash address
#if defined(__FLASHTYPE)
extern unsigned char flash_read(unsigned short addr);
#if EEPROM_SIZE > 0
#define FLASH_READ(addr) \\
(EEADR=(addr)&0xff, \\
EEADRH=(addr)>>8, \\
WREN=0, \\
EECON1 |= 0x80, \\
RD=1, \\
DC=0, \\
DC=0, \\
(EEDATH << 8) | EEDATA)
#else // FLASH_READ without EEPROM
#define FLASH_READ(addr) \\
(EEADR=(addr)&0xff, \\
EEADRH=(addr)>>8, \\
RD=1, \\
DC=0, \\
DC=0, \\
(EEDATH << 8) | EEDATA)
#endif
#endif // end FLASH_READ
// macro FLASH_WRITE used when writing only one word of data
#if __FLASHTYPE==2 || __FLASHTYPE==3
#define FLASH_WRITE(addr,data) \\
do{ \\
unsigned short x=data; \\
flash_((const unsigned char *)&x,1,addr); \\
}while(0)
extern void flash_(const unsigned char * source_addr,unsigned char length,unsigned short dest_addr);
#elif __FLASHTYPE==1
#define FLASH_WRITE(addr, value) \\
EEADR=((addr)&0xff); \\
EEADRH=((addr)>>8); \\
EEDATH=((value)>>8); \\
EEDATA=((value)&0xff); \\
EECON1 |= 0x80; \\
WREN=1; \\
EECON2 = 0x55; \\
EECON2 = 0xaa; \\
WR=1; \\
asm("nop"); \\
asm("nop"); \\
WREN=0
#endif // end FLASH_WRITE
// macro FLASH_ERASE used to clear a 32-Byte sector of flash
#if __FLASHTYPE==3
#define FLASH_ERASE(addr) \\
while(WR)continue; \\
EEADR=((addr)&0xFF); \\
EEADRH=((addr>>8)&0xFF); \\
EECON1=0x94; \\
CARRY=0;if(GIE)CARRY=1;GIE=0;\\
EECON2=0x55;EECON2=0xAA;WR=1; \\
asm("\\tNOP"); \\
if(CARRY)GIE=1
// library function version
extern void flash_erase(unsigned short addr);
#endif // end FLASH_ERASE
/***********************************************************************/
/****** EEPROM memory read/write macros and function definitions *******/
/***********************************************************************/
#if EEPROM_SIZE > 0
#ifdef __FLASHTYPE
// macro versions of EEPROM write and read
#define EEPROM_WRITE(addr, value) \\
while(WR)continue;EEADR=(addr);EEDATA=(value); \\
EECON1&=0x7F;CARRY=0;if(GIE)CARRY=1;GIE=0; \\
WREN=1;EECON2=0x55;EECON2=0xAA;WR=1;WREN=0; \\
if(CARRY)GIE=1
#define EEPROM_READ(addr) ((EEADR=(addr)),(EECON1&=0x7F),(RD=1),EEDATA)
#else // else doesn\'t write flash
#define EEPROM_WRITE(addr, value) \\
while(WR)continue;EEADR=(addr);EEDATA=(value); \\
CARRY=0;if(GIE)CARRY=1;GIE=0; \\
WREN=1;EECON2=0x55;EECON2=0xAA;WR=1;WREN=0; \\
if(CARRY)GIE=1
#define EEPROM_READ(addr) ((EEADR=(addr)),(RD=1),EEDATA)
#endif
/* library function versions */
extern void eeprom_write(unsigned char addr, unsigned char value);
extern unsigned char eeprom_read(unsigned char addr);
#endif // end EEPROM routines
/****************************************************************/
/****** Global interrupt enable/disable macro definitions *******/
/****************************************************************/
#ifdef _PIC16
#ifndef ei
#define ei() (GLINTD = 0) // interrupt disable bit
#endif ei
#if defined(_17C42)
#ifndef di
#define di() { do { GLINTD = 1; } while ( GLINTD == 0 ); } // disable interrupt bit
#endif di
#else
#ifndef di
#define di() (GLINTD = 1) // interrupt disable bit
#endif di
#endif
#elif defined _PIC14
#ifndef ei
#define ei() (GIE = 1) // interrupt enable bit
#endif ei
#if defined(_14000) || defined(_16C61) || defined(_16C62) ||\\
defined(_16C63) || defined(_16C63A) || defined(_16C64) ||\\
defined(_16C65) || defined(_16C65B) || defined(_16C71) ||\\
defined(_16C73) || defined(_16C73B) || defined(_16C74) ||\\
defined(_16C74B) || defined(_16C84) || defined(_16C745) ||\\
defined(_16C765) || defined(_16LC74B)
#ifndef di
#define di() { do { GIE = 0; } while ( GIE == 1 ); } // disable interrupt bit
#endif di
#else
#ifndef di
#define di() (GIE = 0) // interrupt enable bit
#endif di
#endif
#endif
#endif /* _PIC_H */