Integration Manual

Table Of Contents
LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 72 of 182
If RS-232 compatible signal levels are needed, the Maxim 13234E voltage level translator can be used.
This chip translates voltage levels from 1.8 V (module side) to the RS-232 standard.
Figure 37 describes the circuit that should be implemented as if a 1.8 V application processor is used.
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
TP
TP
Figure 37: UART interface application circuit with partial V.24 link (3-wire) in the 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 38.
4
V_INT
TxD
Application processor
(3.0V DTE)
RxD
DTR
DSR
RI
DCD
GND
LISA-U2 series
(1.8V DCE)
15
TXD
12
DTR
16
RXD
9
DSR
10
RI
11
DCD
GND
0 Ω
0 Ω
TP
TP
1V8
B1 A1
GND
U1
VCCB
VCC
A
Unidirectional
Voltage Translator
C1
C2
3V0
DIR1
DIR2 OE
VCC
B2 A2
RTS
CTS
13
RTS
14
CTS
0 Ω
TP
TP
Figure 38: UART interface application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
Reference
Description
Part Number - Manufacturer
C1, C2
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
U1
Unidirectional Voltage Translator
SN74AVC2T245 - Texas Instruments
Table 32: Component for UART application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
If only the TxD and RxD lines are provided, as described in Figure 37 or in Figure 38, and HW flow-
control is disabled (AT&K0), the power saving must be enabled in this way:
AT+UPSV=1: the module automatically enters the low-power idle mode whenever possible and the
UART interface is periodically enabled, as described in section 1.9.2.3, reaching low current
consumption.
With this configuration, when the module is in idle mode, the UART is re-enabled 20 ms after the
first data reception, and the recognition of subsequent characters is guaranteed until the module
is in active mode.
If only TxD and RxD lines are provided, data delivered by the DTE can be lost with these settings:
o HW flow-control enabled in the module (AT&K3, that is the default setting)
o Module power saving enabled by AT+UPSV=1
o HW flow-control disabled in the DTE