u-blox SARA-G3 Series System Integration Manual page 52

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, 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 section 1.9.1.4 for the complete description. For more details, refer to
Manual
[2], AT&K, AT\Q, AT+IFC AT command.
If the hardware flow control is not enabled, the CTS line is always held in the ON state after UART
initialization.
If hardware flow control is enabled, then when the CTS line is ON the UART is enabled and the
module is in active-mode. If the CTS line is OFF it does not necessarily 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 other activities, e.g. network related).
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 will not be a valid communication character (see section 1.9.1.4 for
complete description).
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, refer to
Note [20].
RTS signal behavior
The hardware flow control input (RTS line) is set by default to the OFF state (high level) at UART
initialization. The module then holds the RTS line 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, refer to
AT\Q, AT+IFC command descriptions) the module monitors the RTS line to detect permission from the
DTE to send data to the DTE itself. If the RTS line is set to the OFF state, any on-going data
transmission from the module is immediately interrupted or any subsequent transmission forbidden until the
RTS line changes to the ON state.
The DTE must still be able to accept a certain number of characters after the RTS line is set to
the OFF state: the module guarantees the transmission interruption within two characters from RTS
state change.
If AT+UPSV=2 is set and HW flow control is disabled, the module monitors the RTS line 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
UBX-13000995 - R06
SARA-G3 series - System Integration Manual
u-blox AT Commands Manual
Objective Specification
u-blox AT Commands
Mux Implementation Application
[2] AT&K,
System description
Page 52 of 218