Unused serial outputs on CY7B923 can be either tied to Vcc or left floating to reduce power. One input of unused serial inputs on CY7B933 should be terminated to Vcc through a 1K-5Kohms resistor to assure that no data transitions are accidentally created.
For more information, please refer to "Frequently Asked Question About HOTLink" application note on our website.
HOTLink Transmitter/Receiver (Attached below 38-02017_0D_V)
Frequently Asked Questions about HOTLink (www.cypress.com/cfuploads/support/app_notes/faq.pdf)