User's Manual

SARA-R4 series - System Integration Manual
UBX-16029218 - R03 System description
Page 24 of 94
Flow control handshakes are supported by the UART interface and can be set by appropriate AT commands (see
SARA-R4 series AT Commands Manual [2], &K, \Q AT commands): hardware flow control (over the RTS / CTS
lines), software flow control (XON/XOFF), or none flow control.
Hardware flow control is enabled by default.
The default baud rate is 115200 b/s, while the default frame format is 8N1 (8 data bits, No parity, 1 stop bit: see
Figure 8). Baud rates can be configured by AT command (see SARA-R4 series AT Commands Manual [2]).
The automatic baud rate detection and the automatic frame format recognition are not supported.
D0 D1 D2 D3 D4 D5 D6 D7
Start of 1-Byte
transfer
Start Bit
(Always 0)
Possible Start of
next transfer
Stop Bit
(Always 1)
t
bit
= 1/(Baudrate)
Normal Transfer, 8N1
Figure 8: Description of UART 8N1 frame format (8 data bits, no parity, 1 stop bit)
1.9.1.2 UART signals behavior
At the module switch-on, before the UART interface initialization (as described in the power-on sequence
reported in Figure 5), each pin is first tri-stated and then is set to its relative internal reset state. 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 as AT commands interface.
The configuration and the behavior of the UART signals after the boot sequence are described below. See
section 1.4 for definition and description of module operating modes referred to in this section.
RXD signal behavior
The module data output line (RXD) is set by default to the OFF state (high level) at UART initialization. The
module holds RXD in the OFF state until the module transmits some data.
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 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.
The CTS hardware flow control setting can be changed by AT commands (for more details, see SARA-R4 series
AT Commands Manual [2], AT&K, AT\Q AT commands).