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 107 of 164
Providing the TXD and RXD lines only (not using the complete V24 link)
If the functionality of the CTS, RTS, DSR, DCD, RI and DTR lines is not required in the application, or
the lines are not available, then:
 Connect the module RTS input line to GND or to the CTS output line of the module: since the
module requires RTS active (low electrical level) if HW flow-control is enabled (AT&K3, that is the
default setting), the pin can be connected using a 0
 series resistor to GND or to the
active-module CTS (low electrical level) when the module is in active-mode, the UART interface is
enabled and the HW flow-control is enabled
 Connect the module DTR input line to GND using a 0  series resistor, as 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 (DTE) is used, the circuit that should be implemented as described in
Figure 61 .
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
TP
0
Ω
TP
TP
TP
TP
Figure 61: UART interface application circuit with partial V.24 link (3-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 62 .
5
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
DTR
DSR
RI
DCD
GND
TOBY-L2 series
(1.8V DCE)
16 TXD
13
DTR
17 RXD
10 DSR
11 RI
12
DCD
GND
1V8
B1 A1
GND
U1
VCCB
VCC
A
Unidirectional
Voltage Translator
C1 C2
3V0
DIR1
DIR2 OE
VCC
B2 A2
RTS
CTS
14
RTS
15 CTS
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
TP
0
Ω
TP
TP
TP
TP
Figure 62: UART interface application circuit with partial V.24 link (3-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 SN74AVC2T245
20
- Texas Instruments
Table 37: Component for UART application circuit with partial V.24 link (3-wire) in DTE/DCE serial communication (3.0 V DTE)
20
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