Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 73 of 119
If the functionality of the DSR, DCD and RI lines is not required, or the lines are not available:
• Leave DSR, DCD and RI lines of the module floating, with a test-point on DCD
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.
Figure 42 describes the circuit that should be implemented as if a 1.8 V Application Processor (DTE) is used, given that
the DTE will behave correctly regardless of the DSR input setting.
TxD
Applicat ion Processor
(1.8V 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
Figure 42: UART interface application circuit with partial V.24 link (6-wire) in the 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 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 43, given that the DTE will behave correctly regardless of
the DSR input setting.
4
V_INT
TxD
Applicat ion Processor
(3.0 V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
SARA-R4/N 4
(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
Un idirect ion al
Volt ag e Translat or
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
1V8
B1 A1
GND
U2
VCCBVCCA
Un idirect ion al
Volt age Tr anslat 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
27
- Texas Instruments
U2 Unidirectional Voltage Translator SN74AVC2T245
27
- 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
28
If the functionality of the DSR, DCD, RI and DTR lines is not required, or the lines are not available:
27
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
28
Flow control is not supported by ‘00’, ‘01’ and SARA-R410M-02B-00 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.