Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 57 of 175
1.9.2.2 UART signal behavior
See Table 5 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 18, 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-U2 series Data Sheet [1]. 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 [2].
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 [15].
The CTS hardware flow control setting can be configured by AT commands (for more details, see u-blox AT
Commands Manual [2], 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 LISA-U2 modules "01", "x2" and "68" product versions, the CTS line is always held in the ON state
 on LISA-U2 modules "03" product version onward, 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).