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CIRCUIT DESCRIPTION
CPU (LSI104: HD6433298A42F)
The 16-bit CPU contains a 32k-bit ROM, a 1k-bit RAM, seven 8-bit I/O ports and MIDI interfaces. The CPU receives MIDI message and interprets it using the working storage RAM. For instance, when receiving NOTE ON message, the CPU sends the note number and its velocity to the DSP in order to produce sound of that note. The following table shows the pin functions of LSI104. Pin No. 1 2 3 4 5 6 7 8 9, 10 11, 12 13 14 ~ 20 21 22 23 24 ~30 31 32 33 ~ 48 40 49 ~ 56 57, 58 59 60 61 62 63 64 Terminal P50/TXD P51/RXD P52/SCK -RESET -NMI VCC -STBY VSS XTAL, EXTAL MD1, MD0 AVSS P70 ~ P76 P77 AVCC P60 P61 ~ P67 VCC P27 A0 ~ A14 VSS D0 ~ D7 P40, P41 P42 P43 P44 P45 P46 P47 In/Out � In Out In In In In In In In In In In In Out � In � Out In In/Out � Out Out In � Out � Not used MIDI signal input Reset signal output Reset signal input Power ON trigger signal input +5V source Standby signal input. Connected to +5V. Ground (0V) source 20MHz clock input Mode selection input Ground (0V) source Not used. Connected to ground. DEMO button input signal +5V source LED drive signal output Not used +5V source Not used Address bus Ground (0V) source Data bus Not used. Power ON signal output Read enable signal output Write enable signal output Not used Terminal for 10 MHz clock check point Not used. Connected to +5 V source. Function
DIGITAL SIGNAL PROCESSOR (LSI03: HG51B155FD-1)
Upon receipt of a note number and its velocity, the DSP reads sound and velocity data from the sound source ROM in accordance with the received MIDI message. Then it provides 16-bit serial signal to the DAC. If a control change message or "an effect change" of exclusive message has been received, the DSP adds the effect to the sound data using the effect RAM. The following table shows the pin functions of LSI103.
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