Modem - DTE Connection
Modem does not accept or echo back AT commands
Check that the cable between the serial port of the DTE and the modem is a standard RS232 cable. If the cable is bad, replace it. (Null modem cables, also known as
A limited number of dumb terminals require DCD before they can talk to the modem. If this is the case you have to use a breakout box to raise DCD to the terminal. You can then configure the modems to force DCD using the AT&C0 command.
Check that the character echo command is enabled using the ATE command.
Check that the DTE dialler type configuration option is set to AT. Refer to the AT&M or AT&Q command description.
Check that the response codes configuration option is enabled using the ATQ command.
Make sure that all AT commands are terminated with a carriage return.
Check that the ASCII value of a carriage return matches what is used by the DTE and the modem (defined using
Check that the DTE and modem are using a compatible character format. Valid formats include 8 data bits with no parity, or 7 data bits with even, odd, mark or space parity.
Check that the DTE’s data rate is supported by the modem.
