adv7612 i2c isn't acked, but crystal of 28.636Mhz is working

Hi:

   we are using adv7612 to receive 720p video from top-set box, but the i2c access to adv7612 doesn't work, the detail is as below:

1. we set the VS/FIELD/ALSB pin as being floating, so the IOMAP of adv7612 shoul be 0x98.

2. we use the crystal of 28.636Mhz as the frenquency input, we found that it is working,and  we can probe the 28.636M wave by the scope.

3. we power up the adv7612 by this order: power the 3.3 v firstly, and then 1.8 v after about 10 seconds.

4. the i2c access wave is as below, the wave shows the i2c device address is 0x98, but adv7612 doesn't ack the access.

  so, what is the cause of i2c problem? could you help me? thanks very much.