+V-USB Circuit
+-------------
+ +---+ +---------------+
+USB GND | | ATmega168 |
+=== C3 | |
+5V <-------+--------+---|Vcc,AVCC | PS/2
+ R1 | | ====
+D- <----+--+-----R2-----|INT1 RXD|------->DATA
+D+ <----|---+----R3-----|INT0 XCK|------->CLOCK
+ Z1 Z2 | | ->5V
+GND<----+---+--+--+-----|GND | ->GND
+ | | | |
+ | C2-+--|XTAL1 |
+ | X1 | |
+ +--C3-+--|XTAL2 |
+ +---------------+
+R1: 1.5K Ohm
+R2,R3: 68 Ohm
+Z1,Z2: Zenner 3.6V
+C1,C2: 22pF
+C3: 0.1uF
+X1: Crystal 20MHz(16MHz/12MHz)
+
+