SARA-G450 - System integration manual
UBX-18046432 - R08
Design-in
Page 91 of 143
C1-Public
2.6
Serial interfaces
2.6.1
Primary main serial interface (UART)
2.6.1.1
Guidelines for UART circuit design
Providing the full RS-232 functionality
If RS-232 compatible signal levels are needed, two different external voltage translators can be used
to provide full RS-232 (9 lines) functionality: e.g. using the Texas Instruments SN74AVC8T245PW for
the translation from 1.8 V / 3.0 V to 3.3 V, and the Maxim MAX3237E for the translation from 3.3 V to
an 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
TxD
Application Processor
(1.8V 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
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
21
VSEL
Figure 47: UART application circuit with complete 9-wire link in the DTE/DCE serial communication (1.8 V DTE / 1.8 V DCE)
If a 3.0 V application processor (DTE) is used and module (DCE) generic digital interfaces are
configured to operate at 3.0 V (V_INT = 3 V, if VSEL pin is left unconnected; see
), the circuit
should be implemented as described in
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-G450
(3.0V DCE)
12
TXD
9
DTR
13
RXD
10
RTS
11
CTS
6
DSR
7
RI
8
DCD
GND
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
21
VSEL
Figure 48: UART application circuit with complete 9-wire link in the DTE/DCE serial communication (3.0 V DTE / 3.0 V DCE)
If a 3.0 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
), 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 the 1.8 V supply for the voltage
translators on the module side, as described in