4.4
Crystal oscillator and reset
The
shows the external oscillator circuit; the frequency is 40 MHz.
By setting SB2, SB3 (open) and SB3 (closed) it is possible to drive the EXTAL pin with an external clock.
Figure 6.
Crystal oscillator
XTAL
82
EXTAL
81
GND
SB2
Closed
X1
40MHz
C52
8pF/16V
SB3
Closed
1
2
N
ot
A
ss
em
bl
ed
P1
Header 2
ExtOsc
G
N
D
X_TAL
EX_TAL
C53
8pF/16V
SB4
Closed
The reset circuit is the device STM6315.
The STM6315 (see
) asserts a reset signal whenever the V
CC
pin drops below 2.63 V and keep it
asserted until the level of V
CC
has risen above the threshold for a 210 ms.
Figure 7.
Reset circuit
Vss
1
nRST
2
nMR
3
Vcc
4
U6
ST
M63
15R
DW
13F
GND
GND
GND
R68
1kΩ
LD4
Red
RESET_0
C74
100nF/50V
C75
100nF/50V
R69
2,2kΩ
RESET
SW1
RESET
RESET
VDD_HV_IO_Main
VDD_HV_IO_Main
RESET
Not
Ass
em
ble
d
TP16
Reset
Not Assembled
TP17
GND
GND
1
2
3
JP33
Header 3x1
GND
Deafult: 1-2
The device generates a reset signal when the SW1 button is pressed.
The reset output is an open drain pin and it must be pulled-up to VDD_CPU voltage level (R69). The LD4
provides feedback when the reset pulse is generated.
UM2462
Crystal oscillator and reset
UM2462
-
Rev 3
page 7/25
