Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 100 of 157
4
V_INT
TxD
Application 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
0 Ω
0 Ω
TP
TP
0 Ω
0 Ω
TP
TP
1V8
B1 A1
GND
U1
B3A3
VCCBVCCA
Unidirect ional
Volt age Translat or
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
1V8
B1 A1
GND
U2
VCCBVCCA
Unidirect ional
Volt age Translat or
C3
3V0
DIR1
OE
B2 A2
DIR2
C4
Figure 43: 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
15
- Texas Instruments
U2
Unidirectional Voltage Translator
SN74AVC2T245
15
- Texas Instruments
Table 30: UART application circuit components with partial V.24 link (6-wire) in DTE/DCE serial communication (3.0 V DTE)
Providing the TXD, RXD, RTS and CTS lines only
16
If the functionality of the DSR, DCD, RI and DTR lines is not required, or the lines are not available:
Connect the module DTR input to GND using a 0 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.
15
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
16
Flow control is not supported by ‘00’, ‘01’ and SARA-R410M-02B product versions, but the RTS input must be set low to use the UART on
‘00’ and ‘01’ versions. The DTR input must be set low to have URCs presented over UART on ‘00’, ‘01’ and ‘x2’ product versions.