Ublox SARA-N2 Series, Руководство по системной интеграции

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SARA-N2 / N3 series - System integration manual
UBX-17005143 - R13 Design-in Page 63 of 95
C1-Public
Guidelines for SARA-N2 series modules’ UART lines connection
If RS-232 compatible signal levels are needed, an external voltage translators (e.g. Maxim MAX3237E)
can be used to provide the translation from the
VCC signal level of SARA- N2 modules’ UART interface
(3.3 ÷ 3.6 V) to RS-232 compatible signal level.
If a 3.3 V Application Processor (DTE) is used, which is the preferred solution, the UART interface of
SARA-N2 module can be directly connected with the UART of the DTE as shown in
Figure 39 :
•
Connect DTE TxD output line with the TXD input pin of SARA-N2 modules
• Connect DTE RxD input line with the RXD output pin of SARA-N2 modules
• RTS and CTS lines of the module can be left unconnected and floating, because hardware flow
control is not supported by "02" product version of the SARA-N2 modules
•
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 modules 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 39: SARA- N2 series’ UART interface application circuit with TXD and RXD lines connection to 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 40 .
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 40: SARA- N2 series’ UART interface application circuit with TXD and RXD lines connection to 1.8 V DTE
Reference Description Part number - Manufacturer
C1, C2, C3, C4 100 nF capacitor ceramic X7R 0402 10% 16 V GCM155R71C104KA55 - Murata
U1, U2 Unidirectional voltage translator SN74LVC1T45 - Texas Instruments
Table 23: Parts for SARA- N2 series’ UART interface application circuit with TXD and RXD lines connection to 1.8 V DTE
☞
It is not recommended to use V_INT pin of the SARA-N2 module 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.