请问这段程序是什么意思？

jimmy0524 2008-7-1 16:16 楼主

  US_CR = (1 <<  2) |          /* RSTRX: Reset Receiver: 1 = The receiver logic is reset. */
         (1 <<  3);       /* RSTTX: Reset Transmitter: 1 = The transmitter logic is reset. */
  US_CR = (0 <<  2) |       /* RSTRX: Reset Receiver: 1 = The receiver logic is reset. */
         (0 <<  3) |       /* RSTTX: Reset Transmitter: 1 = The transmitter logic is reset.*/
         (1 <<  4) |       /* RXEN: Receiver Enable: 1 = The receiver is enabled if RXDIS is 0. */
         (0 <<  5) |       /* RXDIS: Receiver Disable: 0 = Noeffect. */
         (1 <<  6) |  /* TXEN: Transmitter Enable: 1 = The transmitter is enabled if TXDIS is 0. */
         (0 <<  7) | /* TXDIS: Transmitter Disable: 0 = Noeffect. */
         (1 <<  8) | /* RSTSTA: Reset Status Bits: 1 = Resets the status bits PARE, FRAME, OVRE and RXBRK in the US_CSR. */
         (0 <<  9) |          /* STTBRK: Start Break: 0 = Noeffect. */
         (0 << 10) |          /* STPBRK: Stop Break: 0 = Noeffect. */
         (0 << 11) |          /* STTTO: Start Time-out: 0 = Noeffect. */
         (0 << 12);
这段程序是什么意思？
如果US_CR的初值是：0x00801A1A,执行完这段程序后，US_CR的值是多少？是怎么得来的？请解答一下好吗，谢谢了！

回复评论（4）

沙发 djsrryd

1<<2可以看作 SETB(US_CR^bit2),

初值对结果没有影响，结果是0x150。

点赞 2008-7-1 19:19

板凳 monica150373637

US_CR  = (1 < <  2) ?       /* RSTRX: Reset Receiver: 1 = The receiver logic is reset. */
         (1 < <  3);       /* RSTTX: Reset Transmitter: 1 = The transmitter logic is reset. */
  US_CR  = (0 < <  2) ?       /* RSTRX: Reset Receiver: 1 = The receiver logic is reset. */
         (0 < <  3) ?       /* RSTTX: Reset Transmitter: 1 = The transmitter logic is reset.*/
         (1 < <  4) ?       /* RXEN: Receiver Enable: 1 = The receiver is enabled if RXDIS is 0. */
         (0 < <  5) ?       /* RXDIS: Receiver Disable: 0 = Noeffect. */
         (1 < <  6) ?  /* TXEN: Transmitter Enable: 1 = The transmitter is enabled if TXDIS is 0. */
         (0 < <  7) ? /* TXDIS: Transmitter Disable: 0 = Noeffect. */
         (1 < <  8) ? /* RSTSTA: Reset Status Bits: 1 = Resets the status bits PARE, FRAME, OVRE and RXBRK in the US_CSR. */
         (0 < <  9) ?          /* STTBRK: Start Break: 0 = Noeffect. */
         (0 < < 10) ?          /* STPBRK: Stop Break: 0 = Noeffect. */
         (0 < < 11) ?          /* STTTO: Start Time-out: 0 = Noeffect. */
         (0 < < 12);

这是在嵌入式中非常通用常见的赋值方式，用的是C特有的“移位”操作，每一个移位其实就是将该位置1(1< 第一步 US_CR = 0x000C;/*0b0000_0000_0000_1100 第2位，第3位为1，其他为0*/
第二步 US_CR = 0x0150; /*0b0000_0001_0101_0000 第4、6、8是1，其他是0*/
最终结果，如果不考虑硬件对其中状态位的改动，结果就是0x0150.

点赞 2008-7-1 21:58