LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 77 of 116
C1-Public
Providing 1 UART with TXD and RXD lines only
☞
Providing the
TXD
and
RXD
lines only is not recommended if the multiplexer functionality is used
in the application: providing also at least the HW flow control (
RTS
/
CTS
lines) is recommended,
and it is in particular necessary if the low power mode is enabled by +UPSV AT command.
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: since the module requires
RTS
active (low electrical
level) if HW flow-control is enabled (AT&K3, which is the default setting).
•
Connect the module
DTR
input to GND, since it may be useful to set
DTR
active if not specifically
handled (see the AT commands manual
, &D, S0, +CSGT, +CNMI AT commands)
•
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, the Maxim MAX13234E voltage level translator can be
used. This chip translates voltage levels from 1.8 V (module side) to the RS-232 standard.
If a 1.8 V Application Processor (DTE) is used, the circuit should be implemented as in
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
LENA-R8 series
(1.8V DCE)
12
TXD
9
DTR
13
RXD
10
RTS
11
CTS
6
DSR
7
RI
8
DCD
GND
0
Ω
TP
0
Ω
TP
Figure 55: UART interface application circuit with partial V.24 link (3-wire) in the DTE/DCE serial communication (1.8 V DTE)
If a 3 V Application Processor (DTE) is used, it is recommended to connect the 1.8 V UART interface
of the module (DCE) by means of appropriate unidirectional voltage translator using the module
V_INT
output as 1.8 V supply for the voltage translator on the module side, as described in
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
DTR
DSR
RI
DCD
GND
LENA-R8 series
(1.8V DCE)
12
TXD
9
DTR
13
RXD
6
DSR
7
RI
8
DCD
GND
1V8
B1
A1
GND
U1
VCCB
VCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR1
DIR2
OE
VCC
B2
A2
RTS
CTS
10
RTS
11
CTS
TP
0
Ω
TP
0
Ω
TP
Figure 56: 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
Various Manufacturers
U1
Unidirectional Voltage Translator
SN74AVC2T245
9
- Texas Instruments
Table 40: Parts for UART application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
9
Voltage translator providing partial power down feature so that the 3 V supply can be ramped up before
V_INT
1.8 V supply