6-4-3
System
Signals
Generating
Circuits
Timing
chart
of
system
signal
generating
circuit
is
written
in
Fig.
6-8
and
each
signals
timing
charts
is
in
Fig.
6-9.
E
signal
(l.008
MHZ)
which
is
inputted
in
IC42
is
shifted
by
clock
generator
l6.l28
MCK,
then
outputted
through
QA,
QB...QH.
By
combining
these
output
signals,
system
signals
are
made.
The
general
explanation
of
each
system
signal
and
their
generating
method
is
explained
in
below.
(1)
CHRCK
(40ch:
IC42
5
Pin,
8Och:
IC35
8
Pin)
The
signal
to
set
the
number
of
display
characters
by
inputting
to
CRTC
block
and
video
signal
generating
block.
For
40
characters,
output
QC
of
IC42
is
used
and
for
80
characters,
the
signal
is
composed
of
QC
and
QG.
(2)
LOAD
(40ch:
IC45
6
Pin,
8Och:
IC35
6
Pin)
LOAD
is
used
for
the
clock
to
latch
the
data
from
store
RAM
and
colour
RAM
to
display
character
unit.
Also,
used
for
the
clock
to
latch
the
data
from
CRTC
and
colour
information
to
display
character
unit.
Further,
the
re-
versed
signal
of
LOAD,
LOAD
signal
is
used
for
the
mode
switch
of
each
character
of
the
synchronious
parallel
load
8
bit
shift
register
(IC
117
HD74LSl66P).
The
signal
for
40
characters
is
composed
of
output
QD
and
QH
of
IC42
and
one
for
80
characters
is
from
QF
and
QG.
(3)
GRENBLE
(40ch:
IC42
13
Pin,
8Och:
IC34
10
Pin)
The
signal
to
control
the
input
signal
to
the
Enable
pin
(output
of
graphic
generator),and
also
to
prevent
the
overlap
of
the
output
of
the
graphic
signal
output
and
character
generator
output.
The
s-gnal
for
40
character
is
composed
of
output
QH
of
IC42,
and
80
characters
if
from
QC
and
QG.
(4)
CAS¢l
(IC28
8_§in)
The
signal
to
give
CAS
signal
(column
address
signal
of
RAM)
to
the
RAM
during
the
display
period
(period
when
E
signal
of
MPU
is
L).
Used
as
a
clock
to
latch
the
display
data
from
RAM
and
is
composed
of
output
QB,
QE
and
QG
of
IC42.
(5)
CAS¢2
(IC46
l3_pin)
The
signal
to
give
CAS
signal
to
the
RAM
during
MPU
period
(during
the
time
when
E
signal
of
MPU
is
H).
Also
used
as
a
signal
for
control
the
Input/
Output
control
of
the
data
in
store
RAM
and
colour
RAM.
Composed
of
E
signal
and
output
QD
of
IC42.
(6)
RAS
(IC46
l
Pin)
The
basic
signal
for
the
RAS
(Row
Address
Signal)
of
RAM.
Also,
used
for
the
switch
of
the
RAM
address.
Composed
of
output
QA,
RC
and
QG
of
IC42.
(7)
MPU
DISPSW
(IC46
4
Pin)
U09
Of
the
SlQn3lS_t
make
thg
RAM
address
change,
composed
of
QB
and
QG
of
IC42
outputs.
Summary of Contents for MB-6890
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