TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 89 of 143
2.6.2
UART interfaces
UART interfaces are not supported by the "50" product version, except for trace logging (diagnostic
purposes) and Ring Indicator functionality over the UART0 interface.
2.6.2.1
Guidelines for UART circuit design
4-wire UART
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 should be implemented as illustrated in Figure 46.
TxD
1.8V Processor / Device
RxD
RTS
CTS
GND
TOBY-L4 series
TXDx
RXDx
RTSx
CTSx
GND
0
Ω
TP
0
Ω
TP
Figure 46: 4-wire UART interface application circuit to connect an external 1.8 V 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 47.
5
V_INT
TxD
3V Processor / Device
RxD
RTS
CTS
GND
TOBY-L4 series
TXDx
RXDx
RTSx
CTSx
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
Figure 47: 4-wire UART interface application circuit to connect an external 3.0V processor / device
Reference
Description
Part Number - Manufacturer
C1, C2
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
U1
Unidirectional Voltage Translator
SN74AVC4T774
16
- Texas Instruments
Table 35: Component for 4-wire UART interface application circuit to connect an external 3.0V processor / device
Test-Points for diagnostic access are recommended to be provided on the UART0
TXD
and
RXD
lines.
They are not required on other UART lines.
16
Voltage translator providing partial power down feature so that the external 3.0 V supply can be ramped up before the
V_INT
1.8 V supply