Korg DDM-110 Service Manual page 14

MSM6235 Terminal Functions
Pin Term
Function
1
RESET Input terminal for interna) initialization.
Low level is active.
2 CLK
Input for timing signal.
3
RD
As long as this input is low, the DO—D7 terminals become outputs, for
reading internal status information to the CPU. However, this is only
enabled when the CS (chip select) terminal is at low level.
4 WR
As long as this input is low, this LSI inputs control words from the CPU
via the data bus and latches the trailing edge. However, the CS terminal
must be low level for this to be enabled.
5 CS
The chip select terminal for this LSI. Low level enables the WR and RD
terminals. High level disables them.
6-13 An 8-bit 2-way data bus terminal connected to the CPU system data bus.
This is used as an output when CS and RD are low. Otherwise it is an input.
18
MIX OUT
(mixed signal output)
Serial output of 4-channel analog signal. This signal is impedance con¬
verted and input to the MIX IN terminal.
20 MIX IN
(mixed signal input)
This input takes the MIX OUT 4-channel serial analog output for separate
output through the OUT 0-3 terminals. The MIX OUT signal is converted
to low impedance before input to this terminal.
22-25 OUT 0-3
Time shared output for each channel from MIX IN input. Uses analog
switching.
14,28 Digital VDD, VSS
Power supply input for digital sections of this LSI.
3) Switch input section and display section.
The DDM-110 and DDM-220 both use the KLM-603 board.
The CPU reads key input data, processes it, and lights the
appropriate LEDs.
Note: This board is the same for the DDM-110 and DDM-
220 but the harness destination is the KLM-602 for
the DDM-110, and the KLM-665 for the DDM-220.
4) Tape interface section.
Used to save digital data from RAM to cassette tape and to
load it back from tape to RAM. For output to tape, the
data is sent using CPU ports P36 and P37. For input to
RAM, the CPU CNTR terminal is used.
5) Tempo oscillator circuit.
This oscillator uses the LM393 (IC10) comparator 1C.
The tempo control FINE knob varies hysteresis and the
COARSE knob adjusts the time constant.
6) Headphone amp.
To avoid unnecessary battery drain, this is designed to oper¬
ate only when headphones are plugged into the jack. So
when performing service procedures remember to plug
headphones into this jack, otherwise the circuit will not
operate.
BA5218A
BLOCK DIAGRAM
MUTE
OUT 1
MUTE
IN
FILTER
BIAS 1
INPUT 1
NFB 1
OUTPUT 1
VCC
7) Power supply section.
To prevent battery leakage, this circuit is designed to cut
off when voltage drops below about 4.6V. C2 is a capacitor
used to maintain voltage for memory backup.
8) Mixer and LPF sections.
Please note that the mixer time constants are different for
the DDM-110 and DDM-220.
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