LISA-U1 series - System Integration Manual
3G.G2-HW-10002-3
Preliminary
System description
Page 46 of 125
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 (for more details please refer to
u-blox AT Commands Manual
[2], AT&K,
AT\Q, AT+IFC AT command) 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 (refer to chapter 1.9.2.3 for the complete description).
If the hardware flow control is not enabled, the
CTS
line is always held in the ON state after UART initialization.
In case of hardware flow control enabled, when
CTS
line is ON the UART is enabled and the module is
in active mode. Instead,
CTS
line to OFF doesn’t necessary mean that the module is in idle-mode, but
only that the UART is not enabled (the module could be forced to stay in active-mode for instance by
USB).
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
idle-mode won’t be a valid communication character (refer to chapter 1.9.2.3 for the complete
description).
When the MUX protocol is active on UART interface, 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 please refer to
Mux Implementation Application
Note
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 please refer to
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.
If AT+UPSV=2 is set and HW flow control is disabled, the
RTS
line is monitored by the module to manage the
power saving configuration:
When an OFF-to-ON transition occurs on the
RTS
input line, the UART is enabled and the module is forced
to active-mode; after 20 ms from the transition the switch is completed and data can be received without
loss. The module can’t enter idle-mode and the UART is keep enabled as long as the
RTS
input line is held in
the ON state
If
RTS
is set to OFF state by the DTE, the module automatically enters idle-mode whenever possible as in the
AT+UPSV=1 configuration (cyclic idle/active mode), but UART is disabled (held in low power mode)
For more details please refer to chapter 1.9.2.3 and
[2], AT+UPSV command.