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SARA-R4 series - System integration manual
UBX-16029218 - R20
Design-in
Page 83 of 128
C1-Public
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)
36
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
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4 series
(1.8V DCE)
12
TXD
9
DTR
13
RXD
10
RTS
11
CTS
6
DSR
7
RI
8
DCD
GND
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 51: 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
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4 series
(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
B3
A3
VCCB
VCCA
Unidirectional
voltage translator
C1
C2
3V0
DIR3
DIR2
OE
DIR1
VCC
B2
A2
B4
A4
DIR4
1V8
B1
A1
GND
U2
B3
A3
VCCB
VCCA
Unidirectional
voltage translator
C3
C4
3V0
DIR1
DIR3
OE
B2
A2
B4
A4
DIR4
DIR2
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 52: 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
37
- Texas Instruments
Table 38: Component for UART application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)
36
Flow control is not supported by SARA-R410M-01B and SARA-R410M-02B-00 product versions. The
RTS
input must be set low to
communicate over UART on SARA-R410M-01B product version. The
DTR
input must be set low to have URCs presented over UART on
SARA-R410M-01B and SARA-R41xM-x2B product versions.
37
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