51中_nop_();是什么意思

在<intrins.h>文件中有定义，下面是具体介绍
_nop_
Summary #include <intrins.h>
void _nop_ (void);

Description The _nop_ routine inserts a NOP instruction into the program. This routine can be used to pause for 1 CPU cycle. This routine is implemented as an intrinsic function. The NOP instruction is included inline.

Return Value None.

Example
#include <intrins.h>
void test_nop (void) {
P1 = 0xFF;

_nop_ (); /* delay for hardware */
_nop_ ();
_nop_ ();

P1 = 0x00;
}

延迟一个时钟周期

不懂吖