SARA-G450 - System integration manual
UBX-18046432 - R08
Design-in
Page 92 of 143
C1-Public
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-G450
(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
1V8
B1
A1
GND
U2
B3
A3
VCCB
VCCA
Unidirectional
voltage translator
C3
C4
3V0
DIR1
DIR3
OE
B2
A2
B4
A4
DIR4
DIR2
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
21
VSEL
Figure 49: UART application circuit with complete 9-wire link in the DTE/DCE serial communication (3.0 V DTE / 1.8 V DCE)
Reference
Description
Part number – Manufacturer
C1, C2, C3, C4
100 nF capacitor ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 – Murata
U1, U2
Unidirectional voltage translator
SN74AVC4T774
14
- Texas Instruments
Table 32: Parts for UART application circuit with complete 9-wire link in DTE/DCE serial interface (3.0 V DTE / 1.8 V DCE)
Providing the TXD, RXD, RTS, CTS and DTR lines only
If the functionality of the DSR, DCD and RI lines is not required, or the lines are not available:
Leave the DSR, DCD and RI lines of the module unconnected and floating
If RS-232 compatible signal levels are needed, two different external voltage translators (e.g. Maxim
MAX3237E and Texas Instruments SN74AVC8T245PW) can be used. The Texas Instruments chip
provides the translation from 1.8 V / 3.0 V to 3.3 V, while the Maxim chip provides the translation from
3.3 V to RS-232 compatible signal level.
If a 1.8 V application processor (DTE) is used and module (DCE) generic digital interfaces are
configured to operate at 1.8 V (V_INT = 1.8 V, if VSEL pin is connected to GND; see
), the circuit
should be implemented as described in
, given that the DTE will behave properly regardless
of the DSR input setting.
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-G450
(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
0
Ω
TP
TP
21
VSEL
Figure 50: UART application circuit with partial V.24 link (6-wire) in the DTE/DCE serial communication (1.8 V DTE / 1.8 V DCE)
14
Voltage translator providing partial power-down feature so that the DTE 3.0 V supply can be also ramped up before V_INT
1.8 V supply