Ublox SARA-N2 Series, System Integration Manual

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SARA-N2 / N3 series - System integration manual
UBX-17005143 - R13 Design-in Page 62 of 95
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Guidelines for SARA-N3 series modules’ TXD and RXD lines connection
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 / 2.8 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 the generic digital interfaces of the module (DCE)
are configured to operate at 1.8 V (
V_INT = 1.8 V, if the VSEL pin is connected to GND; see 1.5.3 ), the
circuit should be implemented as described in Figure 37 .
TxD
Application processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-N3 series
(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
21 VSEL
Figure 37: SARA- N3 series’ UART application circuit with TXD and RXD lines connection (1.8 V DTE / 1.8 V DCE)
If a 2.8 V application processor (DTE) is used, and the generic digital interfaces of the module (DCE)
are configured to operate at 2.8 V (
V_INT = 2.8 V, if the VSEL pin is left unconnected: see 1.5.3 ), the
circuit should be implemented as described in Figure 38 .
TxD
Application processor
(2.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-N3 series
(2.8V DCE)
15
TXD
12 DTR
16
RXD
13
RTS
14
CTS
9 DSR
10 RI
11
DCD
GND
0
Ω
0
Ω
TP
TP
21 VSEL
Figure 38: SARA- N3 series’ UART application circuit with TXD and RXD lines connection (2.8 V DTE / 2.8 V DCE)
If a 3.0 V application processor is used and the generic digital interfaces of the module are configured
to operate at 1.8 V (
V_INT = 1.8 V, if the VSEL pin is connected to GND: see 1.5.3 ), then the 1.8 V UART
of the module (DCE) can be connected to the 3.0 V UART of the application processor (DTE) by means
of an appropriate unidirectional voltage translators providing partial power down feature (thus the
DTE 3.0 V supply can be also ramped up before the module
V_INT 1.8 V supply), using the V_INT supply
output of the module as the 1.8 V supply for the voltage translators on the module side, and the 3.0 V
supply rail application processor on the application processor side.