Akai VS-2EGN

5-5 EXT RAM: IC4
ADDRESS FROM FRON’
—-@»0
PROCESSOR
O-PORT
i
14
>©"* ysisioir
>a
eo
| Dit
DATA
IN/OUT
FROM
pot
FRONT
PROCESSOR
a4 Qi)<— ADDRESS
w@
‘|
FROM
FRONT
PROCESSOR
z@<—.
oo (6)
ce2(7)<— FRON R-SEF(IC2 10 pin}
ook
DATA IN/OUT FROM
FRONT PROCESSOR
L
Pin functions are as follows:
1) Pin() thu eas pin @i): address designation
2) Pin@) thu pin (6: data in/out. Data exchange with
front processor.
3) Pin (7): R.S FF output. When this is connected with
pin and is at HIGH level, RAM operation be-
comes possible.
5-6 LED SCAN
Fig. 7-86 IC4: EXT RAM
4) Pin (9: When this terminal is connected with CE ter-
minal of the front processor and is at LOW level,
RAM is disabled.
5) Pin @0 : W/R terminal. This is connected with WR
terminal of the front processor. Data is read when
this is HIGH, while data is written when this is LOW.
6) Pin @}: Vcc. Normally IDL SV is impressed. B1
(battery) backup (2.4V) in case of power OFF.
ah
—,
Sh
PTF 88Bomow
10L SV
ie oo icy no TT | Diy
ox BSA ef OF OG # & z
1@zl ae |e ¢
or 06
Os 0 = 3 eM
_ Fig. 7-87 LED Control Circuit
FUNCTION-KEY LEO
ri 2a age anf
Po ‘SEGMENT LEO"ON"
Fig. 7-88 Front
Fig.
7-87
shows
the
LED
scan
circuit.
Channel
display
segment
LEDs
and
function
mode
display
LEDs
are
switched
every
2
ms,
and
dynamic
LED
ON
operation
is
performed.
This
is
because
the
contents
of
both
LED
displays
are
controlled
by
the
data
of
the
same
O-port.
In
this
way,
the
number
of
output
pins
of
the
micro-
computer
is
kept
to
a
minimum.
As
shown
in
Fig.
7-88,
TR1
and
TR2
are
alternately
switched
ON
and
OFF
by
PO
and
P1
from
the
microcomputer,
and
the
output
of
the
O-port
of
the
microcomputer
alternately
changes
66
Service Manual VS-2EGN
mak
Processor Py /P, Waveform
between the channel display data and function mode dis-
play data. Since the switching time is as fast as 2 ms,
both appear to be ON at the same time. However, since
ON time of each LED is half that of the static ON condi-
tion, the values of series resistors (R14—R30) are set at
small values. Before access is made to EXT RAM, D/A
converter, CRT controller, etc., all LEDs are turned
OFF. Accordingly, it may sometimes occur at such
time that the LEDs flicker.