Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 58 of 182
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 the 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 the Mux Implementation
Application Note [14].
The CTS hardware flow control setting can be configured by AT commands (for more details, see the
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", "63" 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).
RTS signal behavior
The hardware flow control input (RTS line) is set by default to the OFF state (high level) at UART
initialization. The RTS 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 RTS input.
If the HW flow control is enabled (for more details, see the u-blox AT Commands Manual [2] AT&K,
AT\Q, AT+IFC command description) the RTS line is monitored by the module to detect permission
from the DTE to send data to the DTE itself. If the RTS line is set to OFF state, any on-going data
transmission from the module is immediately interrupted or any subsequent transmission forbidden
until the RTS line changes to ON state.
☞ The DTE must be able to still accept a certain number of characters after the RTS line has been
set to OFF state: the module guarantees the transmission interruption within 2 characters from
RTS state change.