Apalis Carrier Board Design Guide
Toradex AG l Altsagenstrasse 5 l 6048 Horw l Switzerland l +41 41 500 48 00 l
l
Page | 50
Figure 44: External RTC Reference Schematic
2.14.3 Unused I
2
C Signal Termination
All unused I
2
C can be left unconnected if the according I
2
C port is switched off in software.
Otherwise, it is recommended to keep the pull-up resistors available. Unused I
2
C signals can be
configured to be GPIO.
2.15 UART
The Apalis module form factor features up to four UART interfaces. Even though, the UART1 is
specified as a full-featured UART. Some modules might not provide all the control signals. Please
read the relevant datasheet of the modules carefully. The UART1 is the standard console output
interface for the Linux and Windows Embedded Compact operating system. It is desirable to keep
at least the RX and TX signals of this port accessible for system debugging.
UART2 features RTS and CTS signals for hardware flow control while UART3 and UART4 do not
feature any flow control signals. Some modules might provide additional flow control signals on
non-standard pins.
2.15.1 UART Signals
Apalis
Pin
Apalis
Signal Name
I/O
Type
Power
Rail
Description
118
UART1_RXD
I
CMOS
3.3V
Received Data
112
UART1_TXD
O
CMOS
3.3V
Transmitted Data
114
UART1_RTS
O
CMOS
3.3V
Request to Send
116
UART1_CTS
I
CMOS
3.3V
Clear to Send
110
UART1_DTR
O
CMOS
3.3V
Data Terminal Ready
120
UART1_DSR
I
CMOS
3.3V
Data Set Ready
122
UART1_RI
I
CMOS
3.3V
Ring Indicator
124
UART1_DCD
I
CMOS
3.3V
Data Carrier Detect
132
UART2_RXD
I
CMOS
3.3V
Received Data
126
UART2_TXD
O
CMOS
3.3V
Transmitted Data
128
UART2_RTS
O
CMOS
3.3V
Request to Send
130
UART2_CTS
I
CMOS
3.3V
Clear to Send
136
UART3_RXD
I
CMOS
3.3V
Received Data
134
UART3_TXD
O
CMOS
3.3V
Transmitted Data
140
UART4_RXD
I
CMOS
3.3V
Received Data
138
UART4_TXD
O
CMOS
3.3V
Transmitted Data
Table 25: UART Signals
27pF
50V
C154
27pF
50V
C155
GND
100nF
16V
C157
M41T0M6
OSCI
1
OSCO
2
VCC
8
VSS
4
NF
3
OUT
7
SCL
6
SDA
5
IC21
R177
100K
32.768KHz
1
2
OSC2
BAT54
D4
GND
22uF
25V
C156
10R
R174
BAT54
D5
HU2032-LF
+
1
-
2
BAT1
470R
R173
Bac k up during Battery c hange: about 0.6 s ec /uF
MM70-314-310B1
Apalis - I2C
7 of 25
I2C1_SDA
209
I2C1_SCL
211
X1G
I2C1_SCL
I2C1_SDA
3.3V_SW
3.3V
22R
R296
22R
R297
NA
NA
R175
1.8K
R176
1.8K
GND