SARA-G3 series - System Integration Manual
UBX-13000995 - R06
Objective Specification
System description
Page 54 of 218
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
u-blox AT Commands Manual [2], &D AT command).
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
u-blox AT Commands Manual [2] for 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
u-blox AT
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).
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