LARA-R2 series - System Integration Manual
UBX-16010573 - R12
Design-in
Page 104 of 157
Providing the TXD, RXD, RTS, CTS and DTR lines only (not using the complete V.24 link)
If the functionality of the
DSR
,
DCD
and
RI
lines is not required, or the lines are not available:
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, 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 52 illustrates the circuit that should be implemented as if a 1.8 V Application Processor (DTE) is used, given
that the DTE will behave properly regardless of the
DSR
input setting.
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
LARA-R2 series
(1.8V DCE)
15
TXD
12
DTR
16
RXD
13
RTS
14
CTS
9
DSR
10
RI
11
DCD
GND
0
Ω
0
Ω
TP
TP
0
Ω
0
Ω
TP
TP
Figure 52: 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 a
1.8 V supply for the voltage translators on the module side, as described in Figure 53, given that the DTE will
behave properly regardless of the
DSR
input setting.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
LARA-R2 series
(1.8V DCE)
15
TXD
12
DTR
16
RXD
13
RTS
14
CTS
9
DSR
10
RI
11
DCD
GND
0
Ω
0
Ω
TP
TP
0
Ω
0
Ω
TP
TP
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
VCCB
VCCA
Unidirectional
Voltage Translator
C3
3V0
DIR1
OE
B2
A2
DIR2
C4
Figure 53: 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
20
- Texas Instruments
U2
Unidirectional Voltage Translator
SN74AVC2T245
- Texas Instruments
Table 41: Component for UART application circuit with partial V.24 link (6-wire) in DTE/DCE serial communication (3.0 V DTE)
20
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