Hello friends..
I have got serious problem.I have developed an applicatin in which the 89c51 gives output thorugh port 1 pins to a serail to paraller converter ic and that parallel output is latched using a latch ic.port 1 transmits the serial data as well as control the serial/paralled converter and LE signal for latch. I have used optoisolated inputs for controller and two differnt power supplies. One for controller and another is for optocopler driving cirucit which connects to the outside world. My problem is when the power supply of driving circuit is disturbed momentarily, the output data of serial to parallel converter and latch is changed although no such command is given by controller.and the funny thins is that controller is not disturbed,rest of all functions are working satisfactorily. Please give your valuable suggestions.

Regards
Daniel