Ublox SARA-R4 Series, System Integration Manual

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SARA-R4 series - System integration manual
UBX-16029218 - R20 Design-in Page 86 of 128
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Providing the TXD and RXD lines only 42
☞
Providing the TXD and RXD lines only is not recommended if the multiplexer functionality is used
in the application: providing also at least the HW flow control ( RTS and CTS lines) is recommended,
and it is in paricular necessary if the low power mode is enabled by +UPSV AT command.
If functionality of the CTS , RTS , DSR , DCD , RI and DTR lines is not required in the application, then:
•
Connect the RTS input line to GND or to the CTS output line of the module, since the module
requires RTS active (low electrical level) if HW flow-control is enabled (AT&K3, default setting)
• Connect the DTR input line to GND using a 0  series resistor, because it is useful to set DTR active
if not specifically handled, in particular to have URCs presented over the UART interface (see
SARA-R4 series AT commands manual
[2] , &D, S0, +CNMI AT commands)
• Leave DSR , DCD and RI lines of the module floating
If RS-232 compatible signal levels are needed, the Maxim MAX13234E voltage level translator can be
used. This chip translates voltage levels from 1.8 V (module side) to the RS-232 standard.
If a 1.8 V Application Processor (DTE) is used, the circuit that should be implemented as in Figure 57.
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
TP
Figure 57: UART interface application circuit with a 3-wire link in the 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
interface 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 in Figure 58 .
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
DTR
DSR
RI
DCD
GND
SARA-R4 series
(1.8V DCE)
12
TXD
9
DTR
13 RXD
6 DSR
7 RI
8
DCD
GND
1V8
B1 A1
GND
U1
VCCB VCCA
Unidirectional
Voltage Translator
C1 C2
3V0
DIR1
DIR2 OE
VCC
B2 A2
RTS
CTS 10 RTS
11 CTS
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
TP
Figure 58: UART interface application circuit with a partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
Reference Description Part Number - Manufacturer
C1, C2 100 nF Capacitor Ceramic X7R 0402 10% 16 V GRM155R61A104KA01 - Murata
U1 Unidirectional Voltage Translator SN74AVC2T245 43 - Texas Instruments
Table 41: UART application circuit components with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
42 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.
43 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