HMS87C1808B Datasheet, PDF (81/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C1X04B/08B/16B
21. COUNTERMEASURE OF NOISE
21.1 Oscillation Noise Protector
The Oscillation Noise Protector(ONP) is used to supply stable in-
ternal system clock by excluding the noise which could be en-
tered into oscillator and recovery the oscillation fail. This
function could be enabled or disabled by the bit[5] of Configura-
tion Memory (707Fh).
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.
XIN
1
OFP
HF Noise
Observer
Mux
HF Noise
Canceller
0S
XIN_NF
Internal
OSC
0
CLK
Changer
1S
F_INTERNAL
en
INT_CLK
Xin_opt
ONPb = 0
LF_on = 1
IN_CLK = 0
XIN
XIN_NF
INT_CLK reset
INT_CLK
OFP_EN
CHG_END
CLK_CHG
f_INTERNAL
ONPb
LF_on
High Frq. Noise
Noise Cancel
LF Noise
Observer CLK_CHG
en
PS10
o/f
en
OFP
CK _{(8-Bit counter)}
ONPb
IN_CLK
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
SEP. 2004 Ver 1.03
77