what is the meaning of the star on inverter gate?
It looks (based on the link here: http://www.hardwaresecrets.com/printpage/Introduction-to-Logic-Gates/237) like the * means it's an open-collector inverter. "Open collector means that the transistor used on the output of the gate doesn't have its collector internally connected to the integrated circuit's VCC (voltage). So, you have to do this connection by yourself. This means that you need to install an external resistor (called “pull-up”) between the output and VCC to make the circuit work. The good thing is that VCC doesn’t need to be the +5 V power supply. You can install it to a + 12 V power supply and feed your 12 V relay, for example.... open drain is used for CMOS.... Open collector or open drain circuits are usually marked with an asterisk."

Here's an open-drain buffer with a similar (but not identical) symbol: