TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 90 of 143
2-wire UART
If the functionality of the
CTSx
and
RTSx
are not required in the application, or the lines are not available, then:
Consider to connect the module
RTSx
input line to GND or to the
CTSx
output line of the module, since the
module requires
RTSx
active (low electrical level) if HW flow-control is enabled
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 external Processor / Device is used, the circuit that should be implemented as illustrated in Figure 48.
TxD
1.8V Processor / Device
RxD
GND
TOBY-L4 series
TXDx
RXDx
GND
0
Ω
TP
0
Ω
TP
Figure 48: 2-wire UART interface application circuit to connect an external 1.8V processor / device
If a 3.0 V external Processor / Device is used, then it is recommended to connect the 1.8 V UART interface of the
module by means of appropriate unidirectional voltage translators using the module
V_INT
output as a 1.8 V
supply for the voltage translators on the module side, as illustrated in Figure 49.
5
V_INT
TxD
3V Processor / Device
RxD
GND
TOBY-L4 series
TXDx
RXDx
GND
1V8
B1
A1
GND
U1
VCCB
VCCA
Unidirectional
Voltage Translator
C1
C2
3V0
DIR1
DIR2
OE
VCC
B2
A2
TP
0
Ω
TP
0
Ω
TP
Figure 49: 2-wire UART interface application circuit to connect an external 3.0 V processor / device
Reference
Description
Part Number - Manufacturer
C1, C2
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
U1
Unidirectional Voltage Translator
SN74AVC2T245
17
- Texas Instruments
Table 36: Component for 2-wire UART interface application circuit to connect an external 3.0 V processor / device
Test-Points for diagnostic access are recommended to be provided on the UART0
TXD
and
RXD
lines for
diagnostic purposes. Test-Points are not required on other UART lines.
17
Voltage translator providing partial power down feature so that the external 3.0 V supply can be ramped up before
V_INT
1.8 V supply