Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 72 of 119
2.6 Data communication interfaces
2.6.1 UART interface
2.6.1.1 Guidelines for UART circuit design
Providing the full RS-232 functionality (using the complete V.24 link)
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If RS-232 compatible signal levels are needed, two different external voltage translators can be used to provide full RS-
232 (9 lines) functionality: e.g. using the Texas Instruments SN74AVC8T245PW for the translation from 1.8 V to 3.3 V, and
the Maxim MAX3237E for the translation from 3.3 V to RS-232 compatible signal level.
If a 1.8 V Application Processor (DTE) is used and complete RS-232 functionality is required, then the complete 1.8 V UART
of the module (DCE) should be connected to a 1.8 V DTE, as in Figure 40.
TxD
Applicat ion Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4/ N4
(1.8V DCE)
12
TXD
9
DTR
13
RXD
10
RTS
11
CTS
6
DSR
7
RI
8
DCD
GND
0Ω
TP
0Ω
TP
0Ω
TP
0Ω
TP
Figure 40: UART interface application circuit with complete V.24 link in DTE/DCE serial communication (1.8V DTE)
If a 3.0 V Application Processor (DTE) is used, then it is recommended to connect the 1.8 V UART of the module (DCE) 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 41.
4
V_INT
TxD
Applicat ion Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4/ N4
(1.8V DCE)
12
TXD
9
DTR
13
RXD
10
RTS
11
CTS
6
DSR
7
RI
8
DCD
GND
1V8
B1 A1
GND
U1
B3A3
VCCBVCCA
Unidirect ional
Volt ag e Translat or
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
1V8
B1 A1
GND
U2
B3A3
VCCBVCCA
Unidirect ional
Volt ag e Translat or
C3
C4
3V0
DIR1
DIR3 OE
B2 A2
B4A4
DIR4
DIR2
TP
0 Ω
TP
0 Ω
TP
0 Ω
TP
0 Ω
TP
Figure 41: UART interface application circuit with complete V.24 link in DTE/DCE serial communication (3.0 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 SN74AVC4T774
25
- Texas Instruments
Table 29: Component for UART application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)
Providing the TXD, RXD, RTS, CTS and DTR lines only
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Flow control is not supported by ‘00’, ‘01’ and SARA-R410M-02B-00 product versions, but the RTS input must be set low to use the UART on ‘00’ and ‘01’
versions. The DTR input must be set low to have URCs presented over UART on ‘00’, ‘01’ and ‘x2’ product versions.
25
Voltage translator providing partial power down feature so that the DTE 3 V supply can be also ramped up before V_INT 1.8 V supply
26
Flow control is not supported by ‘00’, ‘01’ and SARA-R410M-02B-00 product versions, but the RTS input must be set low to use the UART on ‘00’ and ‘01’
versions. The DTR input must be set low to have URCs presented over UART on ‘00’, ‘01’ and ‘x2’ product versions.