Integration Manual

Table Of Contents
SARA-R5 series - System integration manual
UBX-19041356 - R03 Design-in Page 76 of 123
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Providing 1 UART with the TXD, RXD, RTS and CTS lines only
Compatible with USIO variants 0/1/3; not compatible with USIO variants 2/4 (see section 1.9.1.1).
If the functionality of the DSR, DCD, RI and DTR lines is not required, or the lines are not available:
Leave DSR, DCD, RI and DTR lines of the module floating; it is recommended to provide a test point
on these lines
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 53.
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R5 series
(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
TP
TP
TP
TP
Figure 53: 1 UART interface application circuit with 5-wire link in 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 an appropriate unidirectional voltage translator using the
module V_INT output as 1.8 V supply for the voltage translator on the module side, as in Figure 54.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R5 series
(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
Unidirectional
voltage translator
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
0Ω
TP
0Ω
TP
TP
TP
0Ω
TP
0Ω
TP
TP
TP
TP
Figure 54: 1 UART interface application circuit with 5-wire link 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
GCM155R71C104KA55 - Murata
U1
Unidirectional voltage translator
SN74AVC4T774
9
- Texas Instruments
Table 31: Components for 1 UART application circuit with 5-wire link in DTE/DCE serial communication (3.0 V DTE)
9
Voltage translator providing partial power down feature, so the 3 V supply can be also ramped up before V_INT 1.8 V supply