“char code reserve [3] _at_ 0x23;”是什么语法规则？

lovemcu

“char code reserve [3] _at_ 0x23;”是什么语法规则？ [复制链接]

安装了uVision4之后，打开有个示例程序：

2. /*------------------------------------------------------------------------------
   HELLO.C

3. Copyright 1995-2005 Keil Software, Inc.
   ------------------------------------------------------------------------------*/

4. #include <REG52.H>                /* special function register declarations   */
                                     /* for the intended 8051 derivative         */

5. #include <stdio.h>                /* prototype declarations for I/O functions */

6. 
   #ifdef MONITOR51                         /* Debugging with Monitor-51 needs   */
   char code reserve [3] _at_ 0x23;         /* space for serial interrupt if     */
   #endif                                   /* Stop Exection with Serial Intr.   */
                                            /* is enabled                        */

7. 
   /*------------------------------------------------
   The main C function.  Program execution starts
   here after stack initialization.
   ------------------------------------------------*/
   void main (void) {

8. /*------------------------------------------------
   Setup the serial port for 1200 baud at 16MHz.
   ------------------------------------------------*/
   #ifndef MONITOR51
       SCON  = 0x50;          /* SCON: mode 1, 8-bit UART, enable rcvr      */
       TMOD |= 0x20;               /* TMOD: timer 1, mode 2, 8-bit reload        */
       TH1   = 221;                /* TH1:  reload value for 1200 baud @ 16MHz   */
       TR1   = 1;                  /* TR1:  timer 1 run                          */
       TI    = 1;                  /* TI:   set TI to send first char of UART    */
   #endif

9. /*------------------------------------------------
   Note that an embedded program never exits (because
   there is no operating system to return to).  It
   must loop and execute forever.
   ------------------------------------------------*/
     while (1) {
       P1 ^= 0x01;           /* Toggle P1.0 each time we print */
       printf ("Hello World\n");   /* Print "Hello World" */
     }
   }
   

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请问：

（1）语句“char code reserve [3] _at_ 0x23;   ”初看不符合C语言的语法规则，难道这是51单片机C语言特有的？

（2）没搞明白“P1 ^= 0x01;”起什么作用，我把它注释掉之后，照样运行正常。

 

谢谢！

huo_hu

char code reserve [3] _at_ 0x23;
定义一个char数组位于代码段的0x23地址
P1 ^= 0x01;
^是异或操作，相当于最低位取反

我就是我lxw

P1 ^= 0x01;
就是P1=P1^0x01;

zhq468

受教了:carnation: