SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08
Objective Specification
Design-in
Page 115 of 188
Providing the TXD, RXD, RTS, CTS and DTR lines only (not using the complete V.24 link)
If the functionality of the
DSR
,
DCD
and
RI
lines is not required, or the lines are not available:
Leave
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 SN74AVC4T774) can be used. The Texas Instruments chips provide the translation from
1.8 V to 3.3 V, while the Maxim chip provides the translation from 3.3 V to RS-232 compatible signal level.
Figure 60 describes the circuit that should be implemented as if a 1.8 V application processor is used, given that
the DTE will behave properly regardless
DSR
input setting.
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-G3 / SARA-U2
(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
Figure 60: UART interface application circuit with partial V.24 link (6-wire) in the DTE/DCE serial communication (1.8 V DTE)
If a 3.0 V application processor is used, appropriate unidirectional voltage translators must be provided using the
module
V_INT
output pin as 1.8 V supply, as described in Figure 61, given that the DTE will behave properly
regardless
DSR
input setting.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-G3 / SARA-U2
(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
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
VCCB
VCCA
Unidirectional
Voltage Translator
C3
3V0
DIR1
OE
B2
A2
DIR2
C4
Figure 61: UART interface application circuit with partial V.24 link (6-wire) in DTE/DCE serial communication (3.0 V DTE)
Reference
Description
Part Number - Manufacturer
C1, C2, C3, C4
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
U1
Unidirectional Voltage Translator
SN74AVC4T774 - Texas Instruments
U2
Unidirectional Voltage Translator
SN74AVC2T245 - Texas Instruments
Table 32: Component for UART application circuit with partial V.24 link (6-wire) in DTE/DCE serial communication (3.0 V DTE)