Now Mico8 is successfully implemented on the board. Quick change of logic level at GPIO will produce sound and I made a quick check of "sound generation"
On this board, it is really easy to do it because P28 is connected to piezoelectric sounder through transistor buffer. I just swap MSB of GPIO to piezo out as above.
Code for Mico8 is also very easy. Just fast switching MSB of GPIO (between 0x7F and 0xFF) is enough to make "game shooting sound"... Have fun!