Integration Manual

Table Of Contents
LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 69 of 182
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 unconnected and 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 chip
provides the translation from 1.8 V to 3.3 V, while the Maxim chip provides the translation from 3.3 V
to an RS-232 compatible signal level.
Figure 35 describes the circuit that should be implemented as if a 1.8 V application processor 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
LISA-U2 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 33: 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 is used, appropriate unidirectional voltage translators must be
provided using the module V_INT output pin as a 1.8 V supply, as described in Figure 34, 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
LISA-U2 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
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 34: 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 - Texas Instruments
U2
Unidirectional Voltage Translator
SN74AVC2T245 - Texas Instruments
Table 30: Component for UART application circuit with partial V.24 link (6-wire) in DTE/DCE serial communication (3.0 V DTE)