Andrea,

It may also be possible that your device requires a carriage return or line feed (that Putty is putting in automatically). Maybe try

DeviceWrite[dev, "show_date\n"]

Regards

Ok, here is the code.

I open the port:

dev = DeviceOpen[
  "Serial", {"COM3", "BaudRate" -> 9600, "DataBits" -> 8, 
   "Handshake" -> "XOnXOff", "Parity" -> None, "StopBits" -> 1}]

Now, i turn ON the device, and if it passes the self-test, it sends a code to the serial port, so i read it executing this command:

DeviceReadBuffer[dev]

And here is the answer (correct), translated with ToCharacterCode[]:

ÿ%001000070

Now, i'd like to send a command to de device, like that:

DeviceWrite[dev, "show_date"]

And again i control if device has asnswered, with DeviceReadBuffer:

DeviceReadBuffer[dev]

But there isn't anything in the buffer.

Important: Note that if i send a wrong command to the device, it should answer me with an error message, so, it doesn't receive the command...

Thank you!