Side Note: Almost one and a half years after roman10.com has expired, I decided to start roman10.net. It’s pure technical this time.
AT stands for “Attention”. As lots of modem commands start with these two letters, modem commands are often called AT commands. The AT commands are used to configure the modem and query modem status.
How to Issue AT Commands and View Response
1. Open a terminal window and type “ls /dev/ttyU*” to list all the files created for usb modems. Each of the file represent a modem port/interface.
Normally one interface will be used for control and query, and the other used for data. However, there’re also devices use a single interface for both control and data.
2. Open a terminal tab for each interface. Use “cat /dev/ttyUSB0”, “cat /dev/ttyUSB1” … commands to show the messages. The data interface will be busy and the cat command will fail.
3. Open another terminal, and issue the AT commands echo “AT<commands>^M” > /dev/ttyUSB0, where ^M is Ctrl-v plus Ctrl-m. Example is provided below,
4. The response message should appear on the terminal. The response for the command above is as below,
Some Useful Commands/Info
1. RSSI (Received Signal Strength Indication) Query: +CSQ
echo "AT+CSQ=?^M" > /dev/ttyUSB0 : This will give you the RSSI range
echo "AT+CSQ^M" > /dev/ttyUSB1: This will give you the RSSI value
2. DSFLOWRPT messages (Refer http://www.codeproject.com/KB/IP/3G_Modem_Internet_Dialer.aspx?display=Print
for more info)
Some modems return DSFLOWRPT message every fixed interval (for example, 2 seconds)
This message contains some useful information. A typical DSFLOWRPT message is as below,
0000579A: Connection duration in seconds
00000000: Measured upload speed
00000000: Measured download speed
00000000021B0491: Number of bytes sent
0000000000152275: Number of bytes received
000AFC80: max upload speed
000DCB40: max download speed
More AT commands can be found at 3GPP website http://www.3gpp.org/ and respective modem manufacturer website. Normally modems only support a subset of the AT commands defined in 3GPP standard.