Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 74 of 119
• Connect the module DTR input to GND using a 0 Ω 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 SARA-R4/N4 series AT
Commands Manual [1] for the &D, S0, +CNMI AT commands)
• Leave DSR, DCD and RI lines of the module floating, with a test-point on DCD
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 Figure 44.
TxD
Applicat ion Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4/N4
(1.8V DCE)
12
TXD
9
DTR
13
RXD
10
RTS
11
CTS
6
DSR
7
RI
8
DCD
GND
0Ω
TP
0Ω
TP
0Ω
TP
0Ω
TP
Figure 44: 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 Figure 45.
4
V_INT
TxD
Applicat ion Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4/ N4
(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
B3A3
VCCBVCCA
Unidirect ion al
Volt age Translat or
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
TP
0Ω
TP
0Ω
TP
0Ω
TP
TP
Figure 45: 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
29
- Texas Instruments
Table 31: UART application circuit components with a partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
29
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