3Com AccessBuilder 980/000048/001, User Manual

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3 - 2 C
H A P T E R
3: T
R O U B L E S H O O T I N G
Modem - DTE Connection
Modem does not accept or echo back AT commands
Check t hat 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 cross-over cables, do not work in this application).
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 t hat the character echo command is enabled using the
ATE
command.
Check t hat the DTE dialler type configuration option is set to AT. Refer
to the
AT&M
or
AT&Q
command description.
Check t hat the response codes configuration option is enabled using
the
ATQ
command.
Make sure that all AT commands are terminated with a carriage return.
Check t hat the ASCII value of a carriage return matches what is used by
the DTE and the modem (defined using S-Register
S3
).
Check t hat 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 t hat the DTE’s data rate is supported by the modem.