Casio MG-500 - Page 17

(2)
Peak
Detection
Circuit
‘The
circuit
disregards
abnormal
string
vibration
which
may
occur
at
the
beginning
and
the
end
of
string
vibration
and
detects
the
accurate
frequency
of
string
vibrations.
PEAK
signals
are
provided
at
the
peaks
of
string
vibration
waveform
and
latched
in
the
flip
flops.
While
a
PEAK
signal
is
latched,
output
Q
of
the
flip
flop
rises
to
High
level.
‘At
certain
timing,
CPU
opens
the
tri-state
inverters
by
‘signals
AG
and
7
so
that
data
bus
drop
to
Low.
(CPU
receives
frequency
data
from
the
counters
between
the
period
of
being
Low
of
ADO
-
AD6.
Every
time
CPU
receives
data,
it
compares
the
fre-
soto
quency
with
the
formerly
detected
data
and
if
there
4
,
is
a
difference
between
the
two
data,
CPU
disregards
Ppa
‘the
former
data
in
order
to
detect
the
accurate
fre-
these
date
quency.
When
PEAK
signals
are
not
provided,
Q
outputs
of
the
flip
flops
interrupt
the
CPU
via
INT
1
terminal.
Receiving
INT
I,
CPU
stops
detecting
frequency
data.
High
when
PEAK
signal
is
lotchea
Opens
at
certain
z
timig
PEAK2
when High, CPU
‘does not detect
frequency deta
OINT!
A6,A7©