SARA-R5 series - System integration manual
UBX-19041356 - R04
Design-in
Page 86 of 118
C1-Public
Providing 2 UARTs with the TXD and RXD lines only
☞
Compatible with USIO variants 2/3/4; not compatible with USIO variants 0/1 (see section
☞
Providing the
TXD
and
RXD
lines only is not recommended if the multiplexer functionality is used
in the application: providing also at least the HW flow control (
RTS
and
CTS
lines) is recommended,
and it is in particular necessary if the low power mode is enabled by +UPSV AT command.
If the functionality of the
RTS
,
CTS
,
DSR
and
RI
lines is not required in the application, or the lines are
not available, then:
•
Connect the module
RTS
and
DSR
input lines to GND or respectively to the
CTS
and
RI
output of
the module, since the module requires
RTS
and
DSR
active (low electrical level) if HW flow control
is enabled (as it is by default)
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 (DTE) is used, the circuit should be implemented as in
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
TxD
RxD
RTS
CTS
GND
SARA-R5 series
(1.8V DCE)
12
TXD
(TxD1)
9
DTR
(TxD2)
13
RXD
(RxD1)
10
RTS
(RTS1)
11
CTS
(CTS1)
8
DCD
(RxD2)
6
DSR
(RTS2)
7
RI
(CTS2)
GND
0
Ω
TP
0
Ω
TP
UART1
UART2
0
Ω
TP
0
Ω
TP
Figure 64: 2 UART interfaces application circuit with 3-wire links in DTE/DCE serial communications (1.8 V DTE)
If a 3.0 V application processor (DTE) is used, then it is recommended to connect the 1.8 V UART
interfaces 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
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
TxD
RxD
RTS
CTS
GND
SARA-R5 series
(1.8V DCE)
12
TXD
(TxD1)
9
DTR
(TxD2)
13
RXD
(RxD1)
10
RTS
(RTS1)
11
CTS
(CTS1)
8
DCD
(RxD2)
6
DSR
(RTS2)
7
RI
(CTS2)
GND
1V8
B1
A1
U1
B3
A3
VCCB
VCCA
Unidirectional
voltage translator
C1
C2
3V0
DIR3
DIR1
VCC
B2
A2
B4
A4
GND
OE
DIR4
DIR2
0
Ω
TP
0
Ω
TP
TP
UART1
UART2
0
Ω
TP
0
Ω
TP
Figure 65: 2 UART interfaces application circuit with 3-wire links in DTE/DCE serial communications (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
11
- Texas Instruments
Table 41: Components for 2 UARTs application circuit with 3-wire links in DTE/DCE serial communications (3.0 V DTE)
☞
Provide accessible test points directly connected to
TXD
and
RXD
pins for FW update purpose and
to
DCD
and
DTR
pins for diagnostic purpose.
11
Voltage translator providing partial power down feature, so the 3 V supply can be also ramped up before
V_INT
1.8 V supply