LEXI-R422 - System integration manual
UBX-23007449 - R02
Design-in
Page 72 of 108
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 using a 0
series resistor, since it may be useful to set
DTR
active if not specifically handled, in particular to have URCs presented over the UART
interface (see the AT commands manual
for the &D, S0, +CNMI AT commands)
•
Leave
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
LEXI-R422
(1.8V DCE)
F1
TXD
K1
DTR
E1
RXD
H1
RTS
G1
CTS
M1
DSR
L1
RI
J1
DCD
GND
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 50: UART interface application circuit with partial V.24 link (5-wire) in the DTE/DCE serial communication (1.8V 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 in
A11
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
LEXI-R422
(1.8V DCE)
F1
TXD
K1
DTR
E1
RXD
H1
RTS
G1
CTS
M1
DSR
L1
RI
J1
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
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 51: UART interface application circuit with a partial V.24 link (5-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
SN74AVC4T774
5
- Texas Instruments
Table 32: UART application circuit components with a partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
5
Voltage translator providing partial power down feature so that the DTE 3 V supply can be also ramped up before
V_INT
1.8 V supply
