Integration Manual

Table Of Contents
SARA-R4 series - System integration manual
UBX-16029218 - R20 Design-in Page 85 of 129
C1-Public
Providing the TXD, RXD, RTS, CTS and DTR lines only
38
If the functionality of the DSR, DCD and RI lines is not required, or the lines are not available:
Leave DSR, DCD and RI lines of the module floating
If RS-232 compatible signal levels are needed, two different external voltage translators (e.g. Maxim
MAX3237E and Texas Instruments SN74AVC4T774) can be used. The Texas Instruments chips
provide the translation from 1.8 V to 3.3 V, while the Maxim chip provides the translation from 3.3 V
to RS-232 compatible signal level.
Figure 53 describes the circuit that should be implemented as if a 1.8 V Application Processor (DTE)
is used, given that the DTE will behave correctly regardless of the DSR input setting.
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
0 Ω
TP
TP
0 Ω
0 Ω
TP
TP
Figure 53: UART interface application circuit with partial V.24 link (6-wire) in the DTE/DCE serial communication (1.8 V 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 described in
Figure 54, given that the DTE will behave correctly regardless of the DSR input setting.
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
0 Ω
0 Ω
TP
TP
0 Ω
0 Ω
TP
TP
1V8
B1 A1
GND
U1
B3A3
VCCBVCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
1V8
B1 A1
GND
U2
VCCBVCCA
Unidirectional
Voltage Translator
C3
3V0
DIR1
OE
B2 A2
DIR2
C4
Figure 54: UART interface application circuit with partial V.24 link (6-wire) 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
Unidirectional Voltage Translator
SN74AVC4T774
39
- Texas Instruments
U2
Unidirectional Voltage Translator
SN74AVC2T245
39
- Texas Instruments
38
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.
39
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