u-blox LARA-R2 series System Integration Manual page 39

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 can be changed by AT command (for more details, see u-blox AT
Commands Manual [2], AT&D command description).
If AT+UPSV=3 is set, the DTR line is monitored by the module to manage the power saving configuration (for
more details, see section 1.9.1.4 and u-blox AT Commands Manual [2], AT+UPSV command):

When an OFF-to-ON transition occurs on the DTR input, the UART is enabled and the module is forced to
active-mode. After ~20 ms, the switch is completed and data can be received without loss. The module
cannot enter low power idle-mode and the UART is enabled as long as the DTR is in the ON state

If the DTR input line is set to the OFF state by the DTE, the UART is disabled (held in low power mode) and
the module automatically enters low power idle-mode whenever possible
DCD signal behavior
If AT&C1 is set, as it is by default, 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.
In case of voice calls, DCD is set to the ON state when the call is established.
In case of data calls, there are the following scenarios regarding the DCD signal behavior:

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 see the u-blox AT Commands Manual [2]).
The DCD line is kept in the ON state, even during the online command mode
call is still established even if suspended, while if the module enters command mode
to the OFF state. For more details see DSR signal behavior description.
For scenarios when the DCD line setting is requested for different reasons (e.g. SMS texting during online
command mode
example, in case of SMS texting in online command mode
the SMS command execution is completed (even if the data call release would request DCD set OFF).
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.
10 See the u-blox AT Commands Manual [2] for the definition of the command mode, data mode, and online command mode
UBX-16010573 - R02
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), the DCD line changes to guarantee the correct behavior for all the scenarios. For
LARA-R2 series - System Integration Manual
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, if the data call is released, DCD is kept ON till
Objective Specification
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, to indicate that the data
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, the DSR line is set
System description
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