50ms delay; the program in the general book
Keywords：MCU
Reference address：Assembly delay program for single chip microcomputer
DEL: MOV R7,#200
LO: MOV R6,#123
NOP
L1: DJNZ R6,L1
DJNZ R7,L0
RET
But this program actually delays 50.001ms, one more machine cycle.
In fact, it is impossible to achieve accurate delay with a double loop, so a triple loop must be used.
My program;
DEL: MOV R5,#29
L0: MOV R7,#22
L1: MOV R6,#6
L2: DJNZ R6,L2
DJNZ R7,L1
DJNZ R5,L0
RET
At this time, the precise delay is 50ms, and the values in the three registers can be changed. What we want to discuss here is why it is not possible, or not easy, to use a double loop to implement some precise delay programs, while a triple loop can generally do so. In mathematics, it is the ergodicity of some function values, which is different from the intermediate value of continuous functions due to their continuity. Are there some values that cannot be implemented by a triple loop? So we start using a quadruple loop? What are the necessary and sufficient conditions?
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