User's Manual
TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 103 of 147
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 to GND using a 0 series resistor, since it may be useful to set DTR active if
not specifically handled (see u-blox AT Commands Manual [2], &D, S0, +CSGT, +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 54.
TxD
Application Processor
(1.8V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
TOBY-R2 series
(1.8V DCE)
16
TXD
13
DTR
17
RXD
14
RTS
15
CTS
10
DSR
11
RI
12
DCD
GND
0Ω
TP
0Ω
TP
0Ω
TP
TP
Figure 54: 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 55.
5
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
RTS
CTS
DTR
DSR
RI
DCD
GND
TOBY-R2 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
B3A3
VCCBVCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR3
DIR2 OE
DIR1
VCC
B2 A2
B4A4
DIR4
TP
0Ω
TP
0Ω
TP
0Ω
TP
TP
Figure 55: 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
17
- Texas Instruments
Table 41: Component for UART application circuit with partial V.24 link (5-wire) in DTE/DCE serial communication (3.0 V DTE)
17
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