TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28
Design-in
Page 105 of 164
2.6.2
Asynchronous serial interface (UART)
☞
The UART interface is not available on MPCI-L2 series modules.
2.6.2.1
Guidelines for UART circuit design
☞
The UART interface is not supported by TOBY-L2 modules “00” product versions: all the UART
pins should not be driven by any external device.
Providing the full RS-232 functionality (using the complete V.24 link)
If RS-232 compatible signal levels are needed, two different external voltage translators can be used
to provide full RS-232 (9 lines) functionality: e.g. using the Texas Instruments SN74AVC8T245PW for
the translation from 1.8 V to 3.3 V, and the Maxim MAX3237E for the translation from 3.3 V to RS-232
compatible signal level.
If a 1.8 V Application Processor (DTE) is used and complete RS-232 functionality is required, then the
complete 1.8 V UART interface of the module (DCE) should be connected to a 1.8 V DTE, as described
in
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
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 57: UART interface application circuit with complete V.24 link in 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
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
1V8
B1
A1
GND
U2
B3
A3
VCCB
VCC
A
Unidirectional
Voltage Translator
C3
C4
3V0
DIR1
DIR3
OE
B2
A2
B4
A4
DIR4
DIR2
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
0
Ω
TP
Figure 58: UART interface application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)
Reference
Description
Part Number – Manufacturer
C1, C2, C3, C4 100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 – Murata
U1, U2
Unidirectional Voltage Translator
SN74AVC4T774
18
- Texas Instruments
Table 35: Component for UART application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)
18
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