Ublox SARA-N210, Руководство по системной интеграции

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SARA-N2 series - System Integration Manual
UBX-17005143 - R06 Design-in Page 46 of 82
2.6 Serial interfaces
2.6.1 Asynchronous serial interface (UART)
Guidelines for UART circuit design without RING indication
If a 3.3 V Application Processor (DTE) is used, the UART interface of SARA-N2 module can be directly
connected with the UART interface of the DTE as shown in
Figure 23 :
 Connect DTE TxD output line with the TXD input pin of SARA-N2
 Connect DTE RxD input line with the RXD output pin of SARA-N2
 RTS and CTS lines of the module can be left unconnected and floating, because HW flow control
is not supported by "02" product versions
 Use the same external supply rail (for example, at 3.3 V or 3.6 V) for both the SARA-N2 module and
the Application Processor (DTE), so that the interface of both devices operates at the same level,
considering that the UART interface of SARA-N2 module operates at the VCC voltage level
TxD
Application Processor
(3.3V DTE)
RxD
GND
SARA-N2
(DCE)
12 TXD
13
RXD
GND
0
Ω
TP
0
Ω
TP
52
VCC
3V3 3V3
VCC
51 VCC
53
VCC
Figure 23: UART interface application circuit with partial V.24 link (3-wire) in the DTE/DCE serial communication (3.3 V DTE)
If a 1.8 V Application Processor (DTE) is used, then it is recommended to connect the UART interface
of the module (DCE) by means of appropriate unidirectional voltage translators using the module VCC
line as the supply for the voltage translators on the module side, as described in
Figure 24 .
52
VCC
TxD
Application Processor
(1.8V DTE)
SARA-N2
(DCE)
12
TXD
3V6
B A
GND
U1
VCCB VCCA
Unidirectional
Voltage Translator
C1 C2
1V8
DIR
VCC
0
Ω
TP
51
VCC
53
VCC
RxD
GND
13
RXD
GND
GND
DIR
0
Ω
TP
3V6
B A
U2
VCCB
VCCA
Unidirectional
Voltage Translator
C3
C4
1V8
Figure 24: UART interface application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (1.8 V DTE)
Reference Description Part Number - Manufacturer
C1, C2, C3, C4 100 nF Capacitor Ceramic X7R 0402 10% 16 V GRM155R61A104KA01 - Murata
U1, U2 Unidirectional Voltage Translator SN74LVC1T45 - Texas Instruments
Table 21: Component for UART application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (1.8 V DTE)
☞
It is not recommended to use V_INT pin as control and/or supply line for the external voltage
translator.
☞
It is recommended to provide a direct access to the TXD and RXD lines by means of accessible
testpoints for diagnostic purpose.