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MC80F0104/0204
Preliminary
100
Mar. 2005 Ver 0.2
22. COUNTERMEASURE OF NOISE
22.1 Oscillation Noise Protector
The Oscillation Noise Protector (ONP) is used to supply
stable internal system clock by excluding the noise which
could be entered into oscillator and recovery the oscillation
fail. This function could be enabled or disabled by the
“ONP” bit of the Device configuration area (20FF
H
) for
the MC80F0204, “ONP” option bits MASK option.
The ONP function is like below.
- Recovery the oscillation wave crushed or loss caused
by high frequency noise.
- Change system clock to the internal oscillation clock
when the high frequency noise is continuing.
- Change system clock to the internal oscillation clock
when the X
IN
/X
OUT
is shorted or opened, the main
oscillation is stopped except by stop instruction and
the low frequency noise is entered.
Figure 22-1 Block Diagram of ONP & OFP and Respective Wave Forms
LF Noise
HF Noise
Canceller
HF Noise
Observer
Mux
CLK
Changer
Internal
OSC
OFP
OFP
o/f
CK
PS10
F
INTERNAL
INT_CLK
XIN_NF
XIN
ONP
IN4(2)MCLK(XO)
(8-Bit counter)
en
ONP
OFP
en
en
0
0
1
1
S
S
ONPb = 0
LF_on = 1
IN_CLK = 0
CLK_CHG
XIN_NF
INT_CLK reset
INT_CLK
OFP_EN
CHG_END
CLK_CHG
f
INTERNAL
~ ~
~ ~
~ ~
~ ~
~ ~
~ ~
~ ~
~ ~
~ ~
~ ~
~ ~
High Frq. Noise
XIN
~ ~
~ ~
Noise Cancel
INT_CLK 8 periods
(250ns
×
8 =2us)
Low Frq. Noise or
Oscillation Fail
Clock Change Start(XIN to INT_CLK)
PS10(INT_CLK/512) 256 periods
(250ns
×
512
×
256 =33 ms)
Clock Change End(INT_CLK to XIN))
Observer
Summary of Contents for MC80F0104
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Page 115: ...APPENDIX...
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