Ublox TOBY-L2 series, System Integration Manual

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TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28 Design-in Page 106 of 164
Providing the TXD, RXD, RTS and CTS lines only (not using the complete V.24 link)
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 line to GND using a 0  series resistor, since the module requires
DTR active
 Leave DSR, DCD and RI lines of the module unconnected and floating
If RS-232 compatible signal levels are needed, the Maxim 13234E 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 59 .
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
TOBY-L2 series
(1.8V DCE)
16
TXD
13
DTR
17
RXD
14
RTS
15
CTS
10
DSR
11 RI
12
DCD
GND
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
TP
TP
TP
Figure 59: 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 60 .
5
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
TOBY-L2 series
(1.8V DCE)
16
TXD
13 DTR
17
RXD
14
RTS
15
CTS
10
DSR
11
RI
12
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
0
Ω
TP
0
Ω
TP
TP
TP
TP
Figure 60: 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
19
- Texas Instruments
Table 36: Component for UART application circuit with partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
19
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