User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information Design-in
Page 133 of 206
2.6.2 Auxiliary asynchronous serial interface (UART AUX)
Auxiliary UART interface is not supported by SARA-U2 modules.
2.6.2.1 Guidelines for UART AUX circuit design
The auxiliary UART interface can be connected to an application processor for AT command mode and/or GNSS
tunneling mode supported by SARA-G3 modules product versions “02” onwards. Pass-through mode capability
of the application processor might be considered to provide access to the auxiliary UART interface for SARA-G3
modules’ firmware upgrade by means of the u-blox EasyFlash tool and for diagnostic purpose.
It is highly recommended to provide direct access to the TXD_AUX, RXD_AUX pins of SARA-G3 modules
for execution of firmware upgrade over auxiliary UART using the u-blox EasyFlash tool and for diagnostic
purpose: provide a testpoint on each line to accommodate the access and provide a 0 : series resistor on
each line to detach the module pin from any other connected device.
The circuit with a 1.8 V application processor should be implemented as described in Figure 73.
TxD
Application Processor
(1.8V DTE)
RxD
SARA-G3 series
(1.8V DCE)
29
TXD_AUX
28
RXD_AUX
GND
GND
0 ohm
0 ohm
TestPoint
TestPoint
Figure 73: UART AUX interface application circuit connecting a 1.8 V application processor
If a 3.0 V application processor is used, then it is recommended to connect the 1.8 V auxiliary UART interface of
the module by means of appropriate unidirectional voltage translators using the module V_INT output as 1.8 V
supply for the voltage translators on the module side, as described in Figure 74.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
GND
SARA-G3 series
(1.8V DCE)
29
TXD_AUX
28
RXD_AUX
GND
1V8
B1 A1
GND
U1
VCCBVCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR1
DIR2
OE
VCC
B2 A2
0 ohm
0 ohm
TP
TP
TP
Figure 74: UART AUX interface application circuit connecting a 3.0 V application processor
Reference Description Part Number - Manufacturer
C1, C2
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
U1
Unidirectional Voltage Translator
SN74AVC2T245 - Texas Instruments
Table 47: Component for UART AUX interface application circuit connecting a 3.0 V application processor
See Firmware Update Application Note [28] for additional guidelines regarding the procedure for SARA-G3
modules’ firmware upgrade over the auxiliary UART interface using the u-blox EasyFlash tool.