c51中精确的延时与计算的实现（Precise delay and calculation implementation in C51）.doc

c51中精确的延时与计算的实现（Precise delay and calculation implementation in C51） Precise delay and calculation implementation in C51 C51 due to its readability and portability is very strong, has been widely used in the MCU, but at some point the C51 program in the exact time requirements, would be written in assembly language, but in the precise control of whether C51 can also realize the time? The answer is yes. In C51, there are several ways to achieve accurate time delay One: for a very short delay, required in the US level, using the _nop_ function, this function is a compilation of NOP instructions, delay a few microseconds, insert such a function. Second: for longer delay, requires more than 10us, using C51 in the loop statement to achieve. When you choose a loop statement in C51, you should pay attention to the following questions First, define the cyclic variables in C51, and use unsigned character variables as much as possible. Second, in the FOR statement, how to do as far as possible the use of variable cycle. Third, at do... While, a while statement, the variable is used by the body of the loop method. This is because in the C51 compiler, different loops are used with different instructions. Here are some examples: Unsigned char I; For (i=0; i255; i++); Unsigned char I; For (i=255; I0; i--); Of these, the second loop statement, C51, is compiled with the DJNZ instruction, which corresponds to the following instructions: MOV, 09H, 0FFH LOOP:DJNZ, 09H, LOOP The instructions are fairly concise and well calculated for accurate time delays. Same for do... The same is true in the while and while loop statements Cases: Unsigned char n; N=255; Do{n--} While (n); or N=255; While (n) {n--}; These two loop statements are compiled by C51 to form a method for DJNZ to complete, so it is convenient to calculate the exact time. Third: for the exact delay time is longer, then the loop nesting method is used, so the nested loop method is often used to achieve ms level delay. For loop