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

2019-03-24 19:03发布

安装了uVision4之后，打开有个示例程序：

/*------------------------------------------------------------------------------
HELLO.C
Copyright 1995-2005 Keil Software, Inc.
------------------------------------------------------------------------------*/
#include <REG52.H> /* special function register declarations */
/* for the intended 8051 derivative */
#include <stdio.h> /* prototype declarations for I/O functions */
#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                        */
/*------------------------------------------------
The main C function. Program execution starts
here after stack initialization.
------------------------------------------------*/
void main (void) {
/*------------------------------------------------
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
/*------------------------------------------------
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 "); /* Print "Hello World" */
}
}