TCA8418: reading registers to TCA8418

Part Number:TCA8418

I am using the TCA8418 keybd chip.  I am trying to set the device up.  I can read and write to the confiq register (0x01).   I am addressing the chip with address 0x68. However, writing to any other registers i get back 0x00.  Is there something that i must setup inorder to Read and write to other registers.  i also have a TCA6408 and TCA6416 on my bd.  I am able to read and write correctly  to these devices. I am using the mp430f6736 as my microcontroller.