DB9 Serial communication

I am getting some strange character displays on hyper terminal, after establishing communication with my GSM modem using the appropriate baud rate. When I type "AT", it appears to get开发者_开发技巧 repeated or display strange characters (as though the baud rate were not correct) on the hyper terminal screen as "AATT". And all other AT commands get repeated as well, but what surprises me is that they all respond to the command. "AATT"(having typed "AT") give me "OK".

What could possibly be the problem? I am connecting the Modem to the DB9 using a MAX232. Below is the response

øatt

OK

aaütø

OK

aatt++ücnnmmiiþ?ø

+CNMI: 1,0,0,0,0

OK

aattþ+ccssccss??ø

+CSCS: "UCS2"

OK

RING

RING

RING

NO CARRIER øat++ücnnmmii==11<,22<,00,,00,,00ø OK aattþ+ccssccss==""GGêSMM""ø OK Øaüt++ccmmögæf==11ø OK aatt OK

aaüt++ccþnmii?? +CNMI: 1,2,0,0,0

OK

Thanks!

You have the echo option enabled in your terminal emulator program, so what happens you send the character, your terminal emulator prints it on the screen and at the same time the modem at the other end echos the character back to you so you see it twice.

However, since the mode only gets the character once, it is fine for it.

It's basically a cosmetic problem really. You can fix it if you want by turning off the ehco characters option in your terminal emulator program