解释这段代码/* BIT Register */ /* PSW */ sbit CY = 0xD7; sbit AC = 0xD6; sbit F0 = 0xD5; sbit RS1 = 0xD4; sbit RS0 = 0xD3; sbit OV = 0xD2; sbit P = 0xD0; /* TCON */ sbit TF1 = 0x8F; sbit TR1 = 0x8E; sbit TF0 = 0x8D; sbit TR0 = 0x8C; sbit IE1 = 0x8B; sbit IT1 = 0x8A; sbit IE0 = 0x89; sbit IT0 = 0x88; /* IE */ sbit EA = 0xAF; sbit ES = 0xAC; sbit ET1 = 0xAB; sbit EX1 = 0xAA; sbit ET0 = 0xA9; sbit EX0 = 0xA8; /* IP */ sbit PS = 0xBC; sbit PT1 = 0xBB; sbit PX1 = 0xBA; sbit PT0 = 0xB9; sbit PX0 = 0xB8; /* P3 */ sbit RD = 0xB7; sbit WR = 0xB6; sbit T1 = 0xB5; sbit T0 = 0xB4; sbit INT1 = 0xB3; sbit INT0 = 0xB2; sbit TXD = 0xB1; sbit RXD = 0xB0; /* SCON */ sbit SM0 = 0x9F; sbit SM1 = 0x9E; sbit SM2 = 0x9D; sbit REN = 0x9C; sbit TB8 = 0x9B; sbit RB8 = 0x9A; sbit TI = 0x99; sbit RI = 0x98;

这段代码定义了一些位寄存器（BIT）的地址，这些寄存器是 8051 单片机中用于控制单个位的状态的寄存器。sbit 关键字表示这些寄存器是位寄存器，而 CY、AC、F0、RS1、RS0、OV、P、TF1、TR1、TF0、TR0、IE1、IT1、IE0、IT0、EA、ES、ET1、EX1、ET0、EX0、PS、PT1、PX1、PT0、PX0、RD、WR、T1、T0、INT1、INT0、TXD、RXD、SM0、SM1、SM2、REN、TB8、RB8、TI、RI 分别是对应的位的地址。通过定义这些地址，可以方便地访问这些位寄存器，从而控制单个位的状态，比如设置中断、串口通信、定时器计数等。