原创 51单片机C语言头文件及其使用

               很多初学单片机者往往对C51的头文件感到很神秘，而为什么要那样写,甚至有的初学者喜欢问，P1口的P为什么要大写,不大写行不行呢?其实这样的问题,看过本文后,就会明白。其实这个是在头文件中用sfr定义的，现在定义好了的是这样的sfr P1           = 0x90;，也就是说，到底大写，还是小写，就是在这里面决定的。这就说明，如果你要用小写，就得在头文件中改为小写。其实它都是为了编程序方便才这样写的，在程序编译时，就会变成相应的地址（如P1就变成了0x90）。

                还有一点就是，现在有很多改进型的单片机，它们有很多新增的特殊功能寄存器在标准的reg51.h或reg52.h中没有定义，这就需要自己加进头文件(相关厂家已经把它们定义好了)，当然也可以直接在程序中定义。下面是一个标准的C51头文件：
/*         BYTE Registers         */
sfr P0           = 0x80;
sfr P1           = 0x90;
sfr P2           = 0xA0;
sfr P3           = 0xB0;
sfr PSW          = 0xD0;
sfr ACC          = 0xE0;
sfr B            = 0xF0;
sfr SP           = 0x81;
sfr DPL          = 0x82;
sfr DPH          = 0x83;
sfr PCON         = 0x87;
sfr TCON         = 0x88;
sfr TMOD         = 0x89;
sfr TL0          = 0x8A;
sfr TL1          = 0x8B;
sfr TH0          = 0x8C;
sfr TH1          = 0x8D;
sfr IE           = 0xA8;
sfr IP           = 0xB8;
sfr SCON         = 0x98;
sfr SBUF         = 0x99;

/*         8052 Extensions         */
sfr T2CON         = 0xC8;
sfr RCAP2L = 0xCA;
sfr RCAP2H = 0xCB;
sfr TL2           = 0xCC;
sfr TH2           = 0xCD;

/*         BIT Registers         */
/*         PSW         */
sbit CY           = PSW^7;
sbit AC           = PSW^6;
sbit F0           = PSW^5;
sbit RS1          = PSW^4;
sbit RS0          = PSW^3;
sbit OV           = PSW^2;
sbit P            = PSW^0; //8052 only

/*         TCON         */
sbit TF1          = TCON^7;
sbit TR1          = TCON^6;
sbit TF0          = TCON^5;
sbit TR0          = TCON^4;
sbit IE1          = TCON^3;
sbit IT1          = TCON^2;
sbit IE0          = TCON^1;
sbit IT0          = TCON^0;

/*         IE         */
sbit EA           = IE^7;
sbit ET2          = IE^5; //8052 only
sbit ES           = IE^4;
sbit ET1          = IE^3;
sbit EX1          = IE^2;
sbit ET0          = IE^1;
sbit EX0          = IE^0;

/*         IP         */
sbit PT2          = IP^5;
sbit PS           = IP^4;
sbit PT1          = IP^3;
sbit PX1          = IP^2;
sbit PT0          = IP^1;
sbit PX0          = IP^0;

/*         P3         */
sbit RD           = P3^7;
sbit WR           = P3^6;
sbit T1           = P3^5;
sbit T0           = P3^4;
sbit INT1         = P3^3;
sbit INT0         = P3^2;
sbit TXD          = P3^1;
sbit RXD          = P3^0;

/*         SCON         */
sbit SM0          = SCON^7;
sbit SM1          = SCON^6;
sbit SM2          = SCON^5;
sbit REN          = SCON^4;
sbit TB8          = SCON^3;
sbit RB8          = SCON^2;
sbit TI           = SCON^1;
sbit RI           = SCON^0;

/*         P1         */
sbit T2EX         = P1^1; // 8052 only
sbit T2           = P1^0; // 8052 only
             
/*         T2CON         */
sbit TF2           = T2CON^7;
sbit EXF2          = T2CON^6;
sbit RCLK          = T2CON^5;
sbit TCLK          = T2CON^4;
sbit EXEN2         = T2CON^3;
sbit TR2           = T2CON^2;
sbit C_T2          = T2CON^1;
sbit CP_RL2 = T2CON^0;