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16 Basic Modem Operation
• Multiple AT commands can be combined into one line. For example, AT&D2 and
AT&K0
can be combined into one line AT&D2&K0.
The Comet processes commands from left to right. The AT command that appears to
the right might over-write the command to the left if they are trying to accomplish
tasks or set modes that cannot coexist.
• If you see duplicated characters for each one you type, your Comet and software
both have their
“
echo
”
feature turned. The Comet command echo state is switched
off using ATE0 and on using ATE1 (default). To eliminate the double characters,
turn off the software
’
s command echo rather than using the ATE0 command. If
you see no characters in your terminal window when you type, the modem
’
s echo
setting is probably set to off. In this case, issue the ATE1 command.
• When a command is successfully issued and accepted, a modem responds with
what is called a
“
Result Code.
”
The Comet supports both
“
verbose
”
result codes
(i.e.
“
OK
”
), and
“
numerical
”
result codes (i.e.
“
0").
You can use the ATV command to set it one way or the other as follows:
Command Description
ATV0 Select numerical result code
ATV1 Select verbose result code
There are a few basic commands that do not require the
“
AT
”
command prefix. These
are as follows:
Command Description
A/ Repeats the last issued AT command once
<any key> Terminates the current connection attempt, if pressed
while modem is handshaking.
+++ Escape code sequence. Entered while the modem is
in Data Mode. Returns modem to Command Mode.
The Comet supports several groups of AT commands:
AT Command Set/Type Example
Basic AT commands (compatible) ATB0
Extended AT& commands AT&D0
Extended AT\ commands AT\N3
Extended AT% commands AT%C1
Extended AT- commands AT-C0
S-Register command ATS0=1
S-Register inquiry command ATS0?