In full bridge that is H-Bridge there will be 4 SCRs and you have to turn ON the diagonally placed SCRs at the same time. D1, D2 andf D3, D4 are the diagonal pairs then when D1, D2 is ON D3, D4 will be OFF and vice versa. So, You can tie the gates of D1, D2 and D3, D4. There must be a ZCD circuit to know the ZC. When ZC is detected you send a pulse (firing pulse) to gates of the the diagonal pair of Bridge.
sir refer this.i have used all thad ZCD ADC and varying pulses but not able to get output plz help .i had attached the proteus file and hex file plz run and observe.
Got the signals. What are you trying to do by inputting AC voltage to INT0 pin ? You need a ZCD circuit at the INT0 pin to detect ZC and then fire the SCRs.
To make this circuit properly operative, Zero Crossing Detection is important. From the image it is not understood how you have implemented that detection. Please explain a bit.