Sunday 25 December 2011

Function of signals of 8085.

 Function of signals of 8085.

  (i) HOLD                (ii) HLDA

HOLD and HLDA: HOLD is an active high, input signal used by other controller to request microprocessor about use of address, data and control signals.

The microprocessor in response to HOLD generates a signal to acknowledge the requesting device by HLDA signal. When HLDA is active it indicates that microprocessor has received HOLD request and will relinquish the buses in next clock cycle. The other controller will use buses and upon completion of work will remove HOLD signal, because of this microprocessor will also make HLDA low. The microprocessor takes control of buses half clock cycle after HLDA goes low.

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