LISA-U series - System Integration Manual
UBX-13001118 - R17
Advance information
System description
Page 60 of 190
1.9.2.2
UART signal behavior
See Table 6 for a description of operating modes and states referred to in this section.
At the switch on of the module, before the initialization of the UART interface, as described in the power-on
sequence reported in the Figure 19, each pin is first tri-stated and then is set to its specific internal reset state
that is reported in the pin description table in
LISA-U1 series Data Sheet
[1] and
LISA-U2 series Data Sheet
[2]. At
the end of the boot sequence, the UART interface is initialized, the module is by default in active mode and the
UART interface is enabled. The configuration and the behavior of the UART signals after the boot sequence are
described below.
For a complete description of data and command mode, see the
u-blox AT Commands Manual
RxD signal behavior
The module data output line (
RxD
) is set by default to OFF state (high level) at UART initialization. The module
holds
RxD
in OFF state until no data is transmitted by the module.
TxD signal behavior
The module data input line (
TxD
) is set by default to OFF state (high level) at UART initialization. The
TxD
line is
then held by the module in the OFF state if the line is not activated by the DTE: an active pull-up is enabled
inside the module on the
TxD
input.
CTS signal behavior
The module hardware flow control output (
CTS
line) is set to the ON state (low level) at UART initialization.
If the hardware flow control is enabled, as it is by default, the
CTS
line indicates when the UART interface is
enabled (data can be sent and received). The module drives the
CTS
line to the ON state or to the OFF state
when it is either able or not able to accept data from the DTE over the UART (see 1.9.2.3 for more details).
If hardware flow control is enabled, then when the
CTS
line is OFF it does not necessarily mean that the
module is in low power idle-mode, but only that the UART is not enabled, as the module could be forced
to stay in active-mode for other activities, e.g. related to the network or related to other interfaces.
When the multiplexer protocol is active, the
CTS
line state is mapped to FCon / FCoff MUX command for
flow control issues outside the power saving configuration while the physical
CTS
line is still used as a
power state indicator. For more details, see
Mux Implementation Application Note
The
CTS
hardware flow control setting can be configured by AT commands (for more details, see
u-blox AT
Commands Manual
[3], AT&K, AT\Q, AT+IFC, AT+UCTS AT command).
If the hardware flow control is not enabled, the
CTS
line after the UART initialization behaves as follows:
on all LISA-U modules, except for the “03” product version, the
CTS
line is always held in the ON state
on product version “03” of the LISA-U2 series modules, the
CTS
line is by default set in the ON state, but
can be configured in the OFF state by the AT+UCTS command
When the power saving configuration is enabled and the hardware flow-control is not implemented in the
DTE/DCE connection, data sent by the DTE can be lost: the first character sent when the module is in the
low power idle-mode will not be a valid communication character (see 1.9.2.3 for more details).
