Integration Manual

Table Of Contents
LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 68 of 182
1.9.2.4 UART application circuits
Providing the full RS-232 functionality (using the complete V.24 link)
If RS-232 compatible signal levels are needed to provide full RS-232 (9 lines) functionality, 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.
If a 1.8V application processor is used for complete RS-232 functionality conforming to the ITU
Recommendation [3] in DTE/DCE serial communication, the complete UART interface of the module
(DCE) must be connected to a 1.8 V DTE as described in Figure 31.
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 31: UART interface application circuit with complete V.24 link in DTE/DCE serial communication (1.8V DTE)
If a 3.0 V Application Processor is used, appropriate unidirectional voltage translators must be
provided using the module V_INT output as a 1.8 V supply, as illustrated in Figure 32.
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
B3A3
VCCBVCCA
Unidirectional
Voltage Translator
C3
C4
3V0
DIR1
DIR3 OE
B2 A2
B4A4
DIR4
DIR2
Figure 32: UART interface application circuit with complete V.24 link 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, U2
Unidirectional Voltage Translator
SN74AVC4T774 Texas Instruments
Table 29: Component for UART application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)