LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 75 of 116
C1-Public
Providing 1 UART with TXD, RXD, RTS and CTS lines only
If the functionality of the
DSR
,
DCD
,
RI
and
DTR
lines is not required, or the lines are not available:
•
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
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 is used, the circuit should be implemented as described 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 51: UART interface application circuit with partial V.24 link in the DTE/DCE serial communication (1.8 V DTE)
If a 3.0 V Application Processor (DTE) is used, then it is recommended to connect the 1.8 V UART
interface of the module (DCE) by means of appropriate unidirectional voltage translators using the
module
V_INT
output as 1.8 V supply for the voltage translators on the module side, as described in
4
V_INT
TxD
Application Processor
(3.0V 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
1V8
B1
A1
GND
U1
B3
A3
VCCB
VCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR3
DIR2
OE
DIR1
VCC
B2
A2
B4
A4
DIR4
0
Ω
TP
0
Ω
TP
TP
Figure 52: UART interface application circuit with partial V.24 link 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
SN74AVC4T774
7
- Texas Instruments
Table 38: Parts for UART application circuit with partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
7
Voltage translator providing partial power down feature so that the 3 V supply can be ramped up before
V_INT
1.8 V supply