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10. VCF-VCA + AMP. (output amplifier)
The de-emphasized signal is input to the VCF inside
IC19 (NJM2069) and high-cut; fc, at this time is con
trolled by the analogue data formed by D/A conver
ting the control signal from DDD-1 through PAO to
PA7 of IC17 (82C55). The range of variation is 9 kHz
to 40 kHz. In addition, in the VCA inside the same IC
the output level from IC19 is controlled by analogue
data formed by D/A conversion of the DDD-1 control
signal that has passed through PBO to PB5 of IC17.
SW1 and VR1 which are attached to IC19 are used to
adjust the fc of the built-in VCF. For the detailed ad
specifications manual. The signal output from IC19
passes through the output amplifier formed by IC15,
and then is output to SIG OUT of DDD-1.
This circuit performs clock control of the gate array
(IC7). This control varies the timing inside the gate ar
ray, changing the time for reading data from memory
and the frequency of the sampling clock that is out
put. As a result, the frequency (tune) of the DSB-1
output signal can be varied.
The circuit is an oscillator consisting of the pair tran
sistor Q1, 74HC00 (IC/2) and transistor Q3. By apply
ing a linear control voltage to the pair transistor, the
oscillator is varied exponentially. Since the musical
scale varies exponentially, by control of this circuit
musical intervals can be added to the output signal.
The linear control voltage for the pair transistor is
analogue data formed by D/A conversion of the
DDD-1 control signal output through PAO to PA7 of
IC17 (82C55). The oscillator output frequency varies
within the range of 740 kHz to 3.2 MHz. This range
can be adjusted by VR2, 3 and 4.
12. D-RAM
IC8, IC13, IC14, IC16, IC18, IC21, IC22 and IC24 are
64 K bit dynamic CMOS RAMs; specifically, they are
/iPD4265 which are capable of being backed up by
batteries. There are 4 bits worth of I/O ports for the
memory but this memory has only 1 bit of I/O, so
there are 4 totaling 64k words. Consequently, this cir
cuit which uses 8 has 4 bits x 64k words x 2 blocks
= 128k words. 126 bits (3 words) are used for 1
sampling, which makes 43690 words/12 bits. When
the sampling frequency is taken to be 23.1 kHz, the
maximum delay time of 1891 msec is obtained. Of the
2 blocks, BLOCK 1 uses IC13 as the LSB and also
has IC16, IC21 and IC23 in that order, while BLOCK 2
uses IC8 is the LSB and has IC14, IC18 and IC22 in
that order.
As was discussed in section 12, the memory is divid
ed into 2 blocks. The control signal from DDD-1 is
output to PC3 of IC17 (82C55) and controls IC3
(74HC157) which is used for BLOCK selection, selec
ting either BLOCK 1 or BLOCK 2. If the output from
PC3 of IC17 is "L", reading from and writing into
BLOCK 1 can be done by OE0 or WEO. Also if "H" is
output to PC2 of IC17 (which is normally "L"), making
PC3 "L", reading from and writing into BLOCK 1 can
be done by OE0 or WE0t and continuous (128k
words) reading from and writing into BLOCK 2 can be
done by OE1 or WE1. (PC2 "H" and PC3 "H" are
prohibited by the software. The gate circuit consists
of the three-state buffer consisting of 74HC241 (IC4)
and 74HC244 (IC5), plus HD14572 (IC2). IC4 opens
the gate to either the BLOCK 1 or BLOCK 2 read-out
path as selected by IC 3. The BLOCK read-out path
gates are constantly alternated while the power to
DDD-1 is ON. Both gates are never open at once, but
when the power to DDD-1 is OFF both are closed.
The IC5 gate, due to the way it is coordinated with
IC4, is always closed when the power to DDD-1 is
OFF or when read-out from memory is in progress.
14. BATTERY (battery back-up circuit)
When the power to DDD-1 is ON, DSB-1 is operated
by the power supply voltage supplied from DDD-1.
When the power is OFF, only the memory and
peripheral circuits are operated by the voltage from
the battery, so that the contents of memory are
preserved. Switching between the two modes is done
by transistor Q2.
15. VOLTAGE REGULATOR (stabilized power supply
Inside DSB-1 a stable voltage is produced and sup
plied by IC6 (7805) so that the circuits related to VCO
will not be affected by fluctuations in the DDD-1
power supply voltage.
The DDD-1 data bus writes control data directly into
DO to D7 of IC17 (82C55). These data are output to
PORT A through PORT C, and control DSB-1.
(However, data are read into the data bus side only in
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