u-blox LARA-R2 series System Integration Manual page 38

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 1.9.1.4 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 [21].
The CTS hardware flow control setting can be changed by AT commands (for more details, see u-blox AT
Commands Manual [2], AT&K, AT\Q, AT+IFC, AT+UCTS AT command).
When the power saving configuration is enabled by AT+UPSV command 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 low power idle-mode will not be a valid communication character (see section
1.9.1.4 and in particular the sub-section "Wake up via data reception" for further 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 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, as it is by default, 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 interrupted until the subsequent RTS line change 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.
Module behavior according to RTS hardware flow control status can be configured by AT commands (for more
details, see u-blox AT Commands Manual [2], AT&K, AT\Q, AT+IFC command descriptions).
If AT+UPSV=2 is set and HW flow control is disabled, the module monitors the RTS line to manage the power
saving configuration (For more details, see section 1.9.1.4 and u-blox AT Commands Manual [2], AT+UPSV):

When an OFF-to-ON transition occurs on the RTS input, the UART is enabled and the module is forced to
active-mode. After ~20 ms, the switch is completed and data can be received without loss. The module
cannot enter low power idle-mode and the UART is enabled as long as the RTS is in the ON state

If the RTS input line is set to the OFF state by the DTE, the UART is disabled (held in low power mode) and
the module automatically enters low power idle-mode whenever possible
DSR signal behavior
If AT&S1 is set, as it is by default, the DSR module output line is set by default to the OFF state (high level) at
UART initialization. The DSR line is then set to the OFF state when the module is in command mode
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command mode and is set to the ON state when the module is in data mode
If AT&S0 is set, the DSR module output line is set by default to the ON state (low level) at UART initialization and
is then always held in the ON state.
9 See the u-blox AT Commands Manual [2] for the definition of the command mode, data mode, and online command mode
UBX-16010573 - R02
LARA-R2 series - System Integration Manual
Objective Specification
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