Question

Explain the function of following pins of 8085
(i) HLDA
(ii) SID
(iii) READY

Answer 1

(1) HLDA :
   (a) It is signal for HOLD ACKNOWLEDGEMENT.
   (b) A HLDA output indicates to a peripheral that a HOLD request has been received and that the microprocessor will relinquish control of buses in the next clock cycle.
   (c) After the removal of HOLD request, HLDA goes low.
(2) SID :
   (a) Serial input data. It is a data line for serial input.
   (b) For serial data transmission SID pin is used. For this type of transmission RIM and SIM instructions are used.
(3) READY :
   (a) It is a input signal used by the microprocessor to sense whether a peripheral is ready to transfer data or not.
   (b) This signal is used to delay the microprocessor until a slow responding peripheral is ready to send or accept data.
   (c) If READY is high, the peripheral is ready. If it is low, the microprocessor waits for an integral
   number of clock cycles until it goes high.
   (d) It is used to synchronize slower peripheral to faster microprocessor.