PURPOSE: To secure automatically the synchronism at the side of a receiver, by using two sets of busy detecting parts to detect the presence or absence of a signal between synchronizing pulses.
CONSTITUTION: The synchronizing pulse obtained by a zero cross pulse of a power supply is supplied to the 1st busy detecting part 5 and at the same time divided into 2 parts by a 2-dividing circuit 7 to be converted into a reception synchronizing signal via an EXOR11. When the part 5 detects the presence of a receiving signal that is transmitted with every two zero cross pulses and between synchronizing pulses, the part 5 sets the output of detection at a level H with the next synchronizing pulse. The 2nd busy detecting part 6 which receives the 2-divided synchronizing pulses via the EXOR11 works in the same way as the part 5 and then sets the output at a level H simultaneously with the part 5 if the synchronizing phase has a shift between the receiver and transmitter sides. Under such conditions, a gate 9 produces a short pulse and inverts an FF1 and then the output of the EXOR11 to obtain a normal synchronizing signal which is free from a phase shift.
FUKAGAWA HITOSHI
SUZUKI YOSHIHARU
TANAKA OSAMU
