
Figure 14.
Clock and reset
Clock and Reset Circuitry
Note - External 3.3V
regulator MUST be
enabled when using
oscillator module
SMA style
Connector
Note -
Internal
Pull-Up on
Pin 1
Loop Controlled Pierce
Oscillator Circuit
Connect XTAL jumper to GND when driving EXTAL from
Oscillator Module or External Source
REMOVE XTAL jumper when driving EXTAL from
Oscillator Module or External Source
Reset Circuit
MCU RESET LED
USR RESET LED
Reset-In
Disable
LEGEND
NORMAL TRACE
50 OHM TRACE
50 OHM SAME LENGHT TRACE
AS SHORT AS POSSIBLE TRACE
32kHz Oscillator
External Oscillator
External Clock Input
OS C-MOD
EXTAL-S MA
P ORS T
ES R0
RS T-MCU
RS T-S W
GND
GND
VS S _OS C
GND
GND
GND
GND
GND
GND
VS S _OS C
VS S _OS C
EXTAL
EVB_EXTAL
XTAL
EVB_EXTAL
RS T-S W
ES R0
P ORS T
3.3V_S R
VDD_HV_IO_MAIN
VDD_HV_IO_MAIN
VDD_HV_IO_MAIN
VDD_HV_IO_MAIN
P B4-XTAL32
P E14-EXTAL32
P B4
P E14
C79 100nF 50V
C83 10pF
50V
J 20
S TRIP 2P MD-2MM-O
1
2
R48
4K7
R45
10K
C80 8pF
50V
J 18
S TRIP 2P MD-2MM-O
1
2
J 24
S TRIP 2P MD-2MM
1
2
J 19
S TRIP 3P MD-2MM
1
2
3
GND
Vcc
U6A
74LVC125AMTR
2
3
7
1
4
1
R38
0R
S W1
P us hbutton
R39
DNM
R43
4K7
J 21
S TRIP 2P MD-2MM-O
1
2
J 25
S TRIP 2P MD-2MM
1
2
GND
Vcc
U6B
74LVC125AMTR
5
6
7
1
4
4
Y2
32.768 KHz
1
2
R41
DNM
D1 Ye llow
U5
8MHz
EN
1
GND
2
OUT
3
+Vs
4
GND
Vcc
U6C
74LVC125AMTR
9
8
7
1
4
1
0
R47
4K7
1
2
P 1
S MA-FEM-180
J 22
S TRIP 3P MD-2MM
1
2
3
R46
560R
R36 0R
R40
0R
R44
560R
C81 10pF
50V
GND
VCC
U7
74V1G08S TR
1
2
4
5
3
J 23
S TRIP 2P MD-2MM
1
2
J 17
S TRIP 3P MD-2MM
1
2
3
D2
Re d
C82 8pF
50V
R37
DNM
Y1
40MHz
1
2
R42 50R
UM2731
-
Rev 1
page 29/37
UM2731
Schematic