LISA-U series - System Integration Manual
UBX-13001118 - R17
Advance information
System description
Page 74 of 190
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, that is the default setting),
the pin can be connected using a 0
Ω
series resistor to GND or to the active module
CTS
(low electrical level)
when the module is in active mode, the UART interface is enabled and the HW flow-control is enabled
Connect the module
DTR
input line to GND, to robustly fix the logic level
Leave
DSR
,
DCD
and
RI
lines of the module unconnected and floating
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 38 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-U 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 38: 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 1.8 V supply, as described in Figure 39.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
DTR
DSR
RI
DCD
GND
LISA-U 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
VCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR1
DIR2
OE
VCC
B2
A2
RTS
CTS
13
RTS
14
CTS
0
Ω
TP
TP
Figure 39: 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 33: Component for UART application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
