LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3
Preliminary
System description
Page 45 of 125
1.9.1.2
UART signal behavior (AT commands interface case)
Refer to Table 2 for a description of operating modes and states referred to in this section.
At the module switch-on, before the initialization of the UART interface (each pin is first tristated and then set to
its relative reset state reported in the pin description table in
LEON-G100 / LEON-G200
Data Sheet
[1] (see the
power on sequence description in Figure 19). At the end of the boot sequence, the UART interface is initialized,
the module is by default in active mode and the UART interface is enabled. The configuration and the behavior
of the UART signals after the boot sequence are described below.
For a complete description of data and command mode, refer to
u-blox AT Commands Manual
RxD signal behavior
The module data output line (
RxD
) is set by default to OFF state (high level) at UART initialization. The module
holds
RxD
in OFF state until no data is transmitted by the module.
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 refer to
u-blox AT Commands Manual
[2], AT&K, AT\Q,
AT+IFC commands) the
CTS
line indicates when the module is in active mode and the UART interface is enabled:
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 1.9.1.3 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.
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 1.9.1.3 for the complete
description).
During the MUX mode, 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
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 refer to
u-blox AT Commands Manual
[2] AT&K, AT\Q,
AT+IFC commands) 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 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.
