ZyXEL Communications U-336R/RE User Manual page 139

Problem
Your modem fails to execute AT commands.
Solutions
1. Make sure the DTR LED is ON. If it is OFF, make sure your
communications software is using the same COM port as your
modem.
2. You may have omitted the characters AT from the beginning of
the command line. These characters must appear at the
beginning of each command line.
3. You may have typed the commands when your modem was in
data state instead of the command state. To switch from data
state to command state, type the escape sequence code +++. To
return to the data state, type ATO and press Enter.
Problem
You typed an AT command, but did not receive an OK or 0 result
code.
Solutions
1. Your communications software may be using a different COM
port than your modem. Be sure both the software and your
modem are addressing the same COM port.
2. The E0 and Q1 commands may be in effect, disabling echo and
result codes. To verify this in terminal mode, type AT&V0 and
press Enter with the modem in command state to view the
currently active settings. To enable echo and result codes, type
AT E1 Q0 and press Enter.
3. You may have typed the commands when your modem was in
the data state instead of the command state. To switch from
data state to command state, type the escape sequence code
+++. To return to data state, type ATO and press Enter.
Diagnostics & Troubleshooting 127