When debugging with HyperTerminal, Sim300 did not respond.

I have encountered this problem. Make sure there is nothing wrong with the baud rate. If the baud rate of the module is 0, there is no output information. The command "at" needs to be sent to synchronize the computer with the module. If it is determined to be a fixed baud rate, such as 9600 or 1 15200, it should be possible to communicate after being set on the HyperTerminal. If it still doesn't work, you suspect it's the computer serial port and serial line.

Sometimes you can't connect, and the HyperTerminal is still suspended animation, so you can only fiddle around for a while.