What is the function of ready pin of 8085 microprocessor?

The READY pin on the 8085 microprocessor is used to delay the completion of a bus transfer cycle. It is sampled by the 8085 at the falling edge of clock following ALE. If it is high, the cycle completes. If it is low, the cycle is extended by one clock, with all lines held steady - then it is sampled again at each of the next falling edges of clock until it is high.

The purpose of READY is to allow (usually) memory devices to operate at a slower speed than the 8085.