LARA-R2 series - System Integration Manual
UBX-16010573 - R12
Design-in
Page 106 of 157
Providing the TXD and RXD lines only (not using the complete V24 link)
If the functionality of the
CTS
,
RTS
,
DSR
,
DCD
,
RI
and
DTR
lines is not required in the application, or the lines are
not available:
Connect the module
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, which is the default setting).
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 (DTE) is used, the circuit that should be implemented as described in Figure 56:
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
LARA-R2 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 56: UART interface application circuit with partial V.24 link (3-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 57.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
DTR
DSR
RI
DCD
GND
LARA-R2 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 57: UART interface application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
