Hello Santhi,

The 'clue' is that the 74HC family at 5V is not suited for interfacing with 3V devices, because the Vih for these devices is around 3.5V. If you use 74HCT, you will have no problems, because these have a Vih of 2V.

Again: I have designed several mixed-voltage devices around Cygnal's controllers and haven't had any problems.

Best regards,
Rob