MC80F0804D View Datasheet(PDF) - Unspecified
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MC80F0804D Datasheet PDF : 120 Pages
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MC80F0704/0708/0804/0808
21. COUNTERMEASURE OF NOISE
21.1 Oscillation Noise Protector
The Oscillation Noise Protector (ONP) is used to supply stable
internal system clock by excluding the noise which could be en-
tered into oscillator and recovery the oscillation fail. This func-
tion could be enabled or disabled by the “ONP” bit of the Device
configuration area (20FFH) for the MC80F0704/0708/0804/
0808, “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 XIN/XOUT is shorted or opened, the main
oscillation is stopped except by stop instruction and
the low frequency noise is entered.
XIN
HF Noise
HF Noise
Canceller
1
Mux
0S
OFP
XIN_NF
Internal
0
CLK
Changer
FINTERNAL
Observer
OSC
1S
en
INT_CLK
ONPb = 0
LF_on = 1
IN_CLK = 0
XIN
XIN_NF
INT_CLK reset
INT_CLK
OFP_EN
CHG_END
CLK_CHG
fINTERNAL
ONP
OFP
High Frq. Noise
Noise Cancel
LF Noise
Observer CLK_CHG
en
PS10
en
o/f
OFP
CK (8-Bit counter)
ONP
IN4(2)MCLK(XO)
INT_CLK 8 periods
(250ns × 8 =2us)
PS10(INT_CLK/512) 256 periods
(250ns × 512 × 256 =33 ms)
Low Frq. Noise or
Oscillation Fail
Clock Change Start(XIN to INT_CLK)
Clock Change End(INT_CLK to XIN))
Figure 21-1 Block Diagram of ONP & OFP and Respective Wave Forms
October 31, 2011 Ver 1.03
99
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