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SARA-R5 series - System integration manual
UBX-19041356 - R04
Design-in
Page 81 of 118
C1-Public
2.6
Data communication interfaces
2.6.1
UART interfaces
2.6.1.1
Guidelines for UART circuit design
Providing 1 UART with the full RS-232 functionality (using the complete V.24 link)
☞
Compatible with USIO variant 1; not compatible with USIO variants 0 / 2 / 3 / 4 (see section
).
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 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 complete RS-232 functionality is required, then the
complete 1.8 V UART of the module (DCE) should be connected to a 1.8 V DTE, as in
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
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 54: 1 UART interface application circuit with complete V.24 link in DTE/DCE serial communication (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 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 described in
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
B3
A3
VCCB
VCCA
Unidirectional
voltage translator
C1
C2
3V0
DIR3
DIR2
OE
DIR1
VCC
B2
A2
B4
A4
DIR4
1V8
B1
A1
GND
U2
B3
A3
VCCB
VCCA
Unidirectional
voltage translator
C3
C4
3V0
DIR1
DIR3
OE
B2
A2
B4
A4
DIR4
DIR2
0
Ω
TP
0
Ω
TP
TP
0
Ω
TP
0
Ω
TP
Figure 55: 1 UART interface application circuit with complete V.24 link 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
GCM155R71C104KA55 - Murata
U1, U2
Unidirectional voltage translator
SN74AVC4T774
6
- Texas Instruments
Table 36: Components for 1 UART application circuit with complete V.24 link in DTE/DCE serial communication (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.
6
Voltage translator providing partial power down feature, so the 3 V supply can be also ramped up before
V_INT
1.8 V supply