Figure 15.
Clock and reset
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
0R
0R
32kHz Oscillator
External Oscillator
External Clock Input
GND
GND
VSS_OSC
GND
GND
GND
GND
GND
GND
VSS_OSC
VSS_OSC
GND
EXTAL
EVB_EXTAL
XTAL
EVB_EXTAL
RST-SW
ESR0
PORST
PB4-XTAL32
PE14-EXTAL32
3.3V_SR
VDD_HV_IO_MAIN
VDD_HV_IO_MAIN
VDD_HV_IO_MAIN
VDD_HV_IO_MAIN
C107 10pF
50V
C105 100nF
50V
J 23
STRIP2PMD-2MM
1
2
R41
4K7
R38 10K
J 27
STRIP2PMD-2MM
1
2
J 29
STRIP2PMD-2MM
1
2
J 26
STRIP3PMD-2MM
1
2
3
GND
Vcc
U9A
SN74AHC125DR
2
3
7
14
1
SW1
Pus hbutton
R31
0R
R32
DNM
R36
4K7
J 24
STRIP2PMD-2MM
1
2
J 31
STRIP2PMD-2MM
1
2
R33
DNM
GND
Vcc
U9B
SN74AHC125DR
5
6
7
14
4
Y2
32.768 KHz
1
2
C144
100nF
U6
8MHz
EN
1
GND
2
OUT
3
+Vs
4
D2 Yellow
GND
Vcc
U9C
SN74AHC125DR
9
8
7
14
10
R40
4K7
1
2
P1
SMA-FEM-180
J 28
STRIP3PMD-2MM
1
2
3
R37560R
R30
0R
R34
0R
R39560R
C106 10pF
50V
GND
VCC
U8
74V1G08STR
1
2
4
5
3
J 30
STRIP2PMD-2MM
1
2
J 25
STRIP3PMD-2MM
1
2
3
R29
DNM
D1
Red
Y1
40MHz
1
2
R35 50R
OSC-MOD
EXTAL-SMA
PORST
ESR0
RST-MCU
RST-SW
UM2789
-
Rev 1
page 28/36
UM2789
Schematic
