CYWUSB6935 datasheet says that it is possible to put more than Vcc on input while current is limited beyond 1 mA. So, you need at least 2 kOhms between mega output and CYW input.
For atmega, "logic high" is 0.6Vcc (read datasheet), that is 3 V, so no additional parts required. However, for additional stability conventional NPN can be used.
+5
|
_|_
| |
| | 4K7
|__|
|
|----------------------------------- to ATmega input
| collector
4K7 | /
CYW output ______ base | /
-------------------|______|---------------------||
| | \
| | _\| emmiter
_|_ |
| | 10-20 K |
| | |
--|-- |
| |
--- GND --- GND
OOps, I said justwhat Admin has already said.
