U11 is a monitor of the +5v and provides reset to main CPU, when this voltage falls.
This circuit is used to switch the power supply of Backup SRAM to a battery (BAT1)
simultaneously.
3-5. VASE3 Sound generator
U36, U37 is generator LSI. This LSI reads the wave data from ROM (U38) and outputs it to DSP
and D/A. The upper drawbar, lower drawbar and percussion sounds are mixed. They are sent to
DSP U2. And after being divided into the frequencies of High(HF) and Low(LF), they are sent to
MXH-35A. Pedal BASS is a separate channel.
3-6. DSP
U2 is a Multi-channel dual serial input port DSP. It has a very hi speed (200MHz) internal clocks
and U49 is 1M SRAM. The first half of the DSP receives upper and lower manual digital tone
wheel signals from the VASE3 generator. It adds chorus, vibrato to the drawbars if selected and
then splits the Frequency range in two, HF and LF. The second half of the DSP receives data from
the A/D U31 and adds tone control, expression, digital Leslie and reverb if selected to the signal.
3-7. D/A Converters and A/D Converter
U32, U33, U34 are 24-bit D/A converters. The output of U32 is the upper, lower and percussion
drawbars split into HF and LF these signals will go to the mixer board and then out to the Tube
overdrive circuit PAH-72A. The output of U34 is the Pedals. The output of U33 is the combined
organs output with all effects added split into Left and Right outputs. All of these signals will go
the mixer board.
3-8. Serial Interface, MIDI
U15 (PD71051GU) is a serial interface to U1 main CPU. This interface is for the PEDAL MIDI in.
A photo coupler, U51 (PC400v) is used to couple MIDI IN signals into the serial interface U15.
There is an additional MIDI IN for an added keyboard to be used for lower manual or other MIDI
control of keyboard, it is labeled LM MIDI IN. Photo coupler U50 (PC400v) is used to couple the
MIDI IN signals directly into the CPU. The LM MIDI IN is controlled directly from the Main CPU
thru port 0. Transistor Q2 is used to buffer the MIDI OUT signals generated through CPU output
TxD0. The combination of these circuits allows MIDI merging of the 2 MIDI IN ports.
3-9. LCD (Liquid Crystal Display) Control
The main CPU, U1 controls the LCD (20 character x2 lines).
4. Draw Bar Interface Board (IFH-18A)
ICs U1, U2 and U3 are analog switches that are used to scan 20 channels of analog data from the
