SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 66 of 102
Providing the TXD, RXD, RTS and CTS lines only (not using the complete V.24 link)
9
If the functionality of the
DSR
,
DCD
,
RI
and
DTR
lines is not required in, 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 UART interface (see
SARA-R4 series AT
Commands Manual
[1], &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 33.
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4
(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 33: 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 described in Figure 34.
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4 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
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
TP
Figure 34: UART interface application circuit with 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
10
- Texas Instruments
Table 26: Component for UART application circuit with partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
9
Flow control is not supported by “00”, “01” and “02” product versions, but the
RTS
input has to be set low to communicate over UART.
The
DTR
input of the module has to be set low to have URCs presented over UART interface.
10
Voltage translator providing partial power down feature so that the DTE 3.0 V supply can be also ramped up before
V_INT
1.8 V supply