SARA-G450 - System integration manual
UBX-18046432 - R08
System description
Page 32 of 143
C1-Public
TXD signal behavior
The module data input line (TXD) is set by default to the 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
☞
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.
The CTS hardware flow control setting can be changed by AT commands (for more details, see the
u-blox AT commands manual
, AT&K, AT+IFC, AT+UCTS commands description).
If the hardware flow control is not enabled, after the UART initialization the CTS line behaves as per
AT+UCTS command setting.
☞
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
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 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 hardware 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.
Module behavior according to RTS hardware flow control status can be configured by AT commands
(for more details, see the u-blox AT commands manual
, AT&K, AT+IFC commands description).
