How to understand the for loop delay function in single chip microcomputer

The first for controls the delay_time parameter, that is, how many times does the * * * loop loop internally loop?

The second for (inner loop) completes the control of J from 0 to 199, and * * * loops for 200 times.

Translated into assembly is:

(R0 is the transfer parameter)

Delay:

MOV R 1，#200

DJNZ R 1, USD

DJNZ R0, delay

Soak in water to soften