Korg DSS-1 Service Manual

10. MAIN CIRCUIT EXPLANATION
1. KLM-780
The CPU employs an 8085A-2 (IC21) 8-bit micro
computer; the system clock is 10 MHz. The clock output
is frequency divided by about 2 to give an output fre
quency of about 5 MHz and input to the counter timer in
put terminal of 8155 (IC17). A 1.14 kHz rectangular
waveform is output from 8155 TIMER OUT (PIN 6), so
that interrupt processing is performed for musical scale
data sets for 8 voices, BEND processing, LFO period
etc. (Processing is done 9 times per period.)
The EPROM consists of two 32 KB ICs (IC18 and IC19)
and one 8 KB IC (IC12). The CPU memory space is a
maximum of 64 KB, so the HC74 (IC30) controls
changeover between the two 32 KB EPROMs (IC18,
IC19).
Two 8 KB RAMs (IC11 and IC13) are used. These are
used for program parameter storage and working, and
for multisound parameter storage and working.
An 8155 (IC17) and 8255 (IC14) are used for I/O. The
functions of the ports are as follows.
■8155
PORTA0-A7
PORTB0-B7
PORT CO ~C2
PORTC3-C5
■8255
PORTA0-A7
PORTB0-B3
PORTB4-B7
PORT CO
LCD control data input/output port
Panel LED control signal output
LCD control address output
FDC control signal output
Panel switch DATA INPUT PORT
Panel switch scan OUT PORT
TG WAVEFORM RESOLUTION
Input signal GAIN, ATT control data
output
LS139 (IC28) and LS138 (IC15) respectively have address
decoder functions. IC28 uses the two high-order address
bits A14 and A15, and selects the ROM and RAM chips.
IC15 similarly uses the 3 bits A10 to A12, and outputs the
chipselection YO to Y7 for other chips.
The interface with TG (KLM-782) consists of IC8 (LS245),
IC9 (LS367) and IC10 (LS367).
IC25 (LS374) and IC26 (LS374) from a D TYPE FLIP-
FLOP, configuring 2 complete input/output systems to
the interface circuit with CPU 2 (KLM-781). In addition,
IC32 (LS74) performs CPU interrupt control.
Since the FDD cannot be connected directly to the CPU
bus, an FDC (FLOPPY DRIVE CONTROLLER) is
necessary. In the KLM-780 circuit diagram, IC6 (/*PD765A)
corresponds to the FDC. Also, data read out from the disk
include both CLOCK and DATA which must be separated.
DATA SEPARATOR IC7 (SED9420C) is used for this pur
pose.
The principal functions are as follows. (The FDD control
signal output by the FDC is defined as OUT.)
39
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Korg DSS-1 Specifications

General

Brand	Korg
Model	DSS-1
Category	Synthesizer
Language	English