When I try to write to I2C registers of the ADI HDMI transmitter, the register values do not change.  What is going on?

When Hot-Plug Detect (HPD) is low the HDMI Tx will automatically go into power down mode.

After an HPD interrupt, register 0x41[6] must be set to ‘0’ to power up the part

During power down all registers except for 0x97 – 0xAF are reset to defaults

• These devices will operate same as if HPD = 1 when HPD "override" is enabled
  
  • On the ADV7510, the registers will reset on an HPD = 1 -> 0 transition
  • On the rest of these HDMI Tx devices the registers will not reset on an HPD = 1 -> 0 transition
• HPD state and interrupt registers remain avaiable even of HPD Override is enabled