
UM-0085-B09
DT80 Range User Manual
Page 202
RG
•
DTR hangup
: Whenever the logger wants to hang up a connection it will set the
DTR
(data terminal ready)
signal to inactive. The modem should be set such that it will drop the connection whenever it sees
DTR
inactive.
This behaviour can be set for most modems with the command
AT&D2
.
•
Fixed local baud rate
. Most modems will set their local baud rate automatically ("autobaud") to match that of
the connected device, once it sees an AT command from the device. Some modems, such as some GSM/
CDMA modems, will only autobaud up to a particular maximum rate (such as 19200). To use rates above this
you must set the baud rate to a fixed value using a command to the modem. The way to control this varies
considerably across modems. For example on some modems the command
AT#BDR
can be used to fix the
local baud rate.
To ensure reliable communications with the modem under all conditions it is in fact recommended that you
always fix the modem's baud rate. This should be set to match the baud rate of the DT80's host serial port (by
default 57600). If the modem's baud rate cannot be set then you need to ensure that the logger's
contains at least one AT command so that the modem can autobaud when it is sent.
•
Application specific settings
. You may need to set other settings in the modem that are particular to your
application.
After entering the required configuration settings, it is necessary to tell the modem to store them into its default profile.
This is normally done using the
AT&W
command.
To verify that the settings have been set correctly, power cycle the modem and then send the
AT&V
command to output
the current settings and check that the initialisation commands above have been set for the active profile.
Example
The following initialisation commands are suitable for PSTN modems that use a Rockwell chipset. They may be suitable
for other types as well. Please check the modem's users manual to confirm that it supports all the AT commands
specified here before using these commands.
AT&F
ATE0Q1&D2S0=4&C1&S0\N2%C2&K3#BDR=24
AT&W
Note:
If
DeTransfer
is used to send these commands to the modem then the
\
character must be entered as
\\
. Also note that
because these incantations include a command to fix the baud rate to 57600, the terminal program must be set to 57600 baud,
otherwise the subsequent command (
AT&W
) would not be recognised.
The above AT commands decode as follows:
Command
Description
&F
set all parameters to factory defaults
E0
no echo
Q1
quiet mode (no messages)
&D2
hang up if DTR inactive
S0=4
auto-answer after 4 rings
&C1
DCD follows carrier
&S0
DSR always on
\N2
don't connect unless error correction is active
%C2
enable V42bis data compression
&K3
enable hardware flow control (RTS/CTS)
#BDR=24
set baud rate to 57600 (24 x 2400) – disable autobaud
&W
write settings to default profile
Modem Initialisation String
The DT80 automatically attempts to initialise the device attached to its Host RS 232 port when it first detects the DSR
signal as active and in certain other circumstances. This is done by sending the initialisation string specified by the
INIT
profile key (
HOST_MODEM
section, see
)
The modem should already have been pre-configured (see
), so the recommended
initialisation string is simply
AT
, which is the default.
Sending
AT
will ensure that the modem can autobaud, if it has been configured to do so.