u-blox LARA-R203 System Integration Manual page 105

Providing the TXD, RXD, RTS and CTS lines only (not using the complete V.24 link)
 Connect the module DTR input to GND using a 0  series resistor, since it may be useful to set DTR active if
not specifically handled (see the u-blox AT Commands Manual [2], &D, S0, +CSGT, +CNMI AT commands)

Leave the DSR, DCD and RI lines of the module floating, with a test-point on DCD
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 is used, the circuit should be implemented as described in Figure 54.
Application Processor
(1.8V DTE)
TxD
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
Figure 54: UART interface application circuit with partial V.24 link (5-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 55.
Application Processor
(3.0V DTE)
3V0
VCC
TxD
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
Figure 55: UART interface application circuit with partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
Reference Description
C1, C2 100 nF Capacitor Ceramic X7R 0402 10% 16 V
U1 Unidirectional Voltage Translator
Table 42: Component for UART application circuit with partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
21 Voltage translator providing partial power down feature so that the DTE 3.0 V supply can be also ramped up before V_INT 1.8 V supply
UBX-16010573 - R12
0Ω
TP
0Ω
TP
0Ω TP
TP
Unidirectional
1V8
Voltage Translator
VCCA VCCB
C1
C2
DIR1
DIR3
0Ω
TP
A1 B1
0Ω TP
A2 B2
A3 B3
A4 B4
DIR2 OE
DIR4 GND
U1
0Ω TP
TP
LARA-R2 series - System Integration Manual
LARA-R2 series
(1.8V DCE)
TXD
12
RXD
13
RTS
10
CTS
11
DTR
9
DSR
6
RI
7
DCD
8
GND
LARA-R2 series
(1.8V DCE)
TP
V_INT
4
TXD
12
RXD
13
RTS
10
CTS
11
9 DTR
DSR
6
7 RI
DCD
8
GND
Part Number - Manufacturer
GRM155R61A104KA01 - Murata
SN74AVC4T774 21 - Texas Instruments
Page 105 of 157
Design-in