RESET CIRCUIT
When batteries are set or an AC adapter is connected, the reset IC provides a low pulse to the CPU. The CPU
then initializes its internal circuit.
When the power switch is pressed, the CPU receives a low pulse of POWER signal.The CPU raises APO
signal to +5 V to turn power on.
VDD
Battery set
VDD
POWER
NMIFrom power switch
RESETRSTB CPU
LSI101
Reset ICUPD912GF-3BA
IC106APO
SCKOPower Supply Circuit
RE5VA35AA
POWER SUPPLY CIRCUIT
The power supply circuit generates four voltages as shown in the following table. VDD voltage is always
generated. The others are controlled by APO signal from the CPU.
NameVoltageFor operation of
VDD+5 VCPU, Reset IC, Sound source ROM
AVDD+5.3 VDAC
AVCC+12 VFilter block, Equalizer block
VC+12 VPower amplifier
CPU (LSI101: UPD912GF-3BA)
The 16-bit CPU contains a 1k-byte RAM, three 8-bit I/O ports, two timers, a keycontroller and serial interfaces.
The CPU detects key velocity by counting the time between first-key input signal FI and second-key SI from
the keyboard. The CPU read sound data and velocity data from the sound source ROM in accordance with
the selected tone. Then the CPU provides 16-bit serial sound data to the DAC.The CPU also controls MIDI
input/output and LED driving.
The following table shows the pin functions of LSI101.
Pin No.TerminalIn/OutFunction
1TXD0Out MIDI signal input
2RXD0In MIDI signal output
3SCK0Out APO (Auto Power Off) signal output
4 ~ 6N Not used. Connected to ground.
7AVCCIn Ground (0 V) source
8, 9AN0, AN1N Not used. Connected to ground.
10AGNDIn Ground (0 V) source
11BCKOut Bit clock output
12SOOut Serial sound data output
13LRCKOut Word clock output
14GNDIn Ground (0 V) source
N 5 N |
ACEC
