Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 59 of 175
DCD signal behavior
If AT&C0 is set, the DCD module output line is set by default to 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 OFF state (high level) at UART initialization. The
DCD line is then set by the module in accordance with the carrier detect status: ON if the carrier is detected, OFF
otherwise. In case of voice call DCD is set to ON state when the call is established. For a data call there are the
following scenarios (see the u-blox AT Commands Manual [2] for the definition of the interface data mode,
command mode and online command mode):
 PSD 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
 CSD 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
In case of a voice call DCD is set to ON state on all the serial communication interfaces supporting the AT
command interface. (including MUX virtual channels, if active).
DCD is set to ON during the execution of a command requiring input data from the DTE (all the
commands where a prompt is issued; see AT commands +CMGS, +CMGW, +USOWR, +USODL,
+UDWNFILE in u-blox AT Commands Manual [2]). The DCD line is set to 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.
DCD line is kept to 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 DSR line is set to OFF state. For
more details see the DSR signal behavior description.
In case of scenarios for which 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 will be kept to ON till the SMS command execution is completed (even if the data call release
would request the DCD setting to OFF).