u-blox SARA-G3 Series System Integration Manual page 54

DTR signal behavior
The DTR module input line is set by default to the OFF state (high level) at UART initialization. The
module then holds the DTR line in the OFF state if the line is not activated by the DTE: an active pull-
up is enabled inside the module on the DTR input. Module behavior according to DTR status depends on
the AT command configuration (see
DCD signal behavior
If AT&C0 is set, the DCD module output line is set by default to the ON state (low level) at UART
initialization and is then always held in the ON state.
If AT&C1 is set, the DCD module output line is set by default to the OFF state (high level) at UART
initialization. The module then sets the DCD line according to the carrier detect status: ON if the carrier
is detected, OFF otherwise. For voice calls, DCD is set to the ON state when the call is established. For
a data call there are the following scenarios (refer to the
definition of the interface data mode, command mode and online command mode):
 Packet Switched Data call: Before activating the PPP protocol (data mode) a dial-up application must
provide the ATD*99***<context_number># to the module: with this command the module switches
from command mode to data mode and can accept PPP packets. The module sets the DCD line to
the ON state, then answers with a CONNECT to confirm the ATD*99 command. The DCD ON is not
related to the context activation but with the data mode

Circuit Switched Data call: To establish a data call, the DTE can send the ATD<number> command to
the module which sets an outgoing data call to a remote modem (or another data module). Data
can be transparent (non reliable) or non transparent (with the reliable RLP protocol). When the
remote DCE accepts the data call, the module DCD line is set to ON and the CONNECT
<communication baudrate> string is returned by the module. At this stage the DTE can send
characters through the serial line to the data module which sends them through the network to the
remote DCE attached to a remote DTE
The DCD is set to ON during the execution of the +CMGS, +CMGW, +USOWR, +USODL AT
commands requiring input data from the DTE: the DCD line is set to the ON state as soon as the
switch to binary/text input mode is completed and the prompt is issued; DCD line is set to OFF
as soon as the input mode is interrupted or completed (for more details refer to the
Commands Manual
[2]).
The DCD line is kept in the ON state, even during the online command mode, to indicate that the
data call is still established even if suspended, while if the module enters command mode, the DSR
line is set to the OFF state. For more details refer to
description.
For scenarios when the DCD line setting is requested for different reasons (e.g. SMS texting during
online command mode), the DCD line changes to guarantee the correct behavior for all the
scenarios. For instance, in case of SMS texting in online command mode, if the data call is
released, the DCD line is kept to ON till the SMS command execution is completed (even if the
data call release would request the DCD setting to OFF).
UBX-13000995 - R06
SARA-G3 series - System Integration Manual
u-blox AT Commands Manual
u-blox AT Commands Manual
DSR signal behaviorDSR signal behavior
Objective Specification
[2], &D AT command).
[2] for the
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System description
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