CASIO MT-36
MT-200
MT-90
CT-102		   digital squarewave keyboards with unusual percussion

These are the keyboards with Casio's bipolar multipulse squarewave sound engine. With their linear volume envelopes, the sound style is Casio's closest equivalent to MC-3, although timbre and percussion quality is one notch higher. Unfortunately the envelopes end too soon, and there is no fingered chord mode in any of these keyboards.

Casio MT-36

This simple beginners keyboard of 1985 has only 4 rhythms and 6 sounds, but features unusual semi- digital percussion (resembling Casio SK-1). The rhythms always insert a fill-in every 4th bar, and there is a single finger accompaniment (but no manual chord mode).

Unusual is that the case plastic is not black but a very dark blue. A white version of this instrument was released as Casio MT-35 and Realistic Concertmate 400. The original German retail price of the Casio MT-35 in a German Casio prospect of 1985 and Conrad catalogue of 1986 was 299DM (about 150€).

main features:

eastereggs:

modifications:

  • polarity protection diode added, power supply jack polarity corrected.

    • notes:

    Although the rectangular OBS sound and rhythm select buttons look like locking switches, they don't lock. The main voice timbres resemble Casio VL-Tone 1 and thus are quite unrealistic. The preset sounds are all made from bipolar multipulse squarewave (pulses can go up or down) with different pulse patterns and none of them features vibrato (not even in vibraphone), nor there is a button to enable vibrato separately.

    The percussion of the rhythm features an unusual metallic clicking hihat (made from semi-metallic shift register feedback noise) that strongly resembles Casio SK-1. The dull base drum sounds unspectacular. Also the snare is a bit dull but has a nicely grainy POKEY timbre (mixing both shift register noises). But these are no typical blip percussion, because their decay envelopes are shaped by a capacitor that prevents zipper noise. Unusual is that despite partly digital percussion, this instrument still has a real analogue tempo slider (can be set from very low to quite high). The combination of squarewave sounds with polyphony and digital percussion is quite unusual for Casio, because they normally used "Consonant-Vowel Synthesis" (2 mixed squarewaves with independent envelopes) in their older polyphonic instruments (see Casio CT-410V for explanation) and sample based timbres in later ones. So this sound engine was likely designed as a cheaper alternative to integrate main voice, accompaniment and percussion into a single sound IC.

    Despite there is a single finger chord accompaniment, this instrument has no manual chord mode; when the "casio chord" slide switch is on, the thing always starts rhythm when any chord section keys are hit. The rhythm always automatically inserts a fill-in (with accompaniment track when on) every 4th bar; this stupid feature also existed in some Yamaha keyboards (e.g. PS-30 and MP-1), but unlike there it can not even be turned off.
     

    circuit bending details

    The Casio MT-36 is based on the CPU "Toshiba TMP8049P, 3437" (clocked @ 4.96 MHz) with sound IC "Hitachi HD43720" and semi-analogue percussion.
    This hardware has strong similarities with CT-102, thus for details see there. The main difference is that it is not crystal clocked and has auto-power-off, and of course the CPU has different software.

    keyboard matrix

    This keyboard matrix was examined by me, based on the service manual of Casio CT-102. The matrix outputs from the CPU are routed through inverters (2x "TC4049BP").
     
    12 KI1
    13 KI2
    14 KI3
    15 KI4
    16 KI5
    17 KI6
    18 KI7
    19 KI8
     
    CPU pin
    in 1
    in 2
    in 3
    in 4
    in 5
    in 6
    in 7
    in 8
    in / out
     
    o
    C1
    o
    C#1
    o
    D1
    o
    D#1
    o
    E1
    o
    F1
    O.
    piano
    R.
    rock
    out 1
    /27 KC1
    o
    F#1
    o
    G1
    o
    G#1
    o
    A1
    o
    A#1
    o
    B1
    O.
    elec. piano
     R.
    swing
    out 2
    /28 KC2
    o
    C2
    o
    C#2
    o
    D2
    o
    D#2
    o
    E2
    o
    F2
    O.
    organ
    R.
    bossa nova
    out 3
    /29 KC3
    o
    F#2
    o
    G2
    o
    G#2
    o
    A2
    o
    A#2
    o
    B2
    O.
    oboe
    R.
    waltz
    out 4
    /30 KC4
    o
    C3
    o
    C#3
    o
    D3
    o
    D#3
    o
    E3
    o
    F3
    O.
    clarinet
     R.
    rock+F
    out 5
    /31 KC5
    o
    F#3
    o
    G3
    o
    G#3
    o
    A3
    o
    A#3
    o
    B3
    O.
    vibraphone
    R.
    swing+F
    out 6
    /32 KC6
    o
    C4
    o
    C#4
    o
    D4
    o
    D#4
    o
    E4
    o
    F4
     O.
    strings
     R.
    bossa nova+F
    out 7
    /33 KC7
     o
    F#4
    o
    G4
    o
    G#4
    o
    A4
    o
    A#4
    o
    B4
     O.
    elec. organ
     R.
    waltz+F
    out 8
    /34 KC8
    o
    C5
    -
    C.
    single finger
    -
    -
    R.
    start/stop
    demo
    power off
    out 9
    /35 KC9

    The input lines are active-low, i.e. react on GND. Any functions can be triggered by a non- locking switch in series to a diode from one "in" to one "out" pin.

    The matrix inputs of CPU pins 12..16 are multiplexed with the sound IC data bus and thus may make strange sounds when fed with wrong signal timing.
     

    legend:
    "o"
    		 = keyboard key
    underlined
    		 = function needs locking switch (i.e. stays active only so long the switch is closed)
    R.
    		 = preset rhythm
    O.
    		 = preset sound ('orchestra')
    C.
    		 = chord
    orange
    background     		 = easteregg (unconnected feature)

    Unlike my expectation I did neither find a manual chord mode nor sustain. Apparently the MT-36 software was rewritten from scratch and not based on MT-200 or CT-102.
     

    connector CN1

    pin  
    1 KC9
    2 KC6 
    3 KC5 
    4 KC4 
    5 KC3
    6 KC2
    7 KC1
    8  
    9  
    10  
    11  
    		Because the matrix outputs are routed through inverters, they are a little difficult to find. But they are also at a foil cable CN1 (pins numbered bottom up) to the right of the PCB.

    2 of the pins are at the inverter IC "TC4049-2" near the CPU (KC-7=pin 12, KC-8=pin 10).

    Thus in the following I refer to matrix pin names instead of CPU pin numbers. Regard that my notes of this are incomplete and may be faulty. The matrix inputs are at the CPU.

    • more preset sounds
      Wire each a button through a diode at KI7->KC7 and KI7->KC8 for additional preset sounds 'strings' and 'elec. organ'.
    • rhythms with manual fill-in
      This feature is most interesting and works very similar like in Casio PT-80. Rewire the rhythm buttons to KI8-> {KC5, KC8, KC7, KC8} (or install additional buttons) to get each a manual fill-in by holding them. The 'rock' fill-in resembles boogie. Unfortunately I found no method to disable the automatic fill-in, that will still sound every 4 bars.

    According to the manual, the demo of MT-36 is the German folk song "Unterlanders Heimweh", but the melody is very different from the wonderful song of that name on ROM-Pack RO-551 (which corresponds to the famous demo of Casio VL-1 and was likely misnamed - read more about this unofficial Casio anthem here). I identified the MT-36 song as "Drunten im Unterland" (means "Down in the Lowlands", ©1835 by Gottfried Weigle, seen on YouTube with German lyrics) aka "Unterländers Heimweh" (regard the 'ä'). The MT-36 melody sounds like a rural folk waltz and resembles a bit "Little Brown Jug". The simple folk waltz tune is only a very short monoto that cycles through all 6 preset sounds again and again without any complex accompaniment changes or the like, but at least you can play to it or change the preset sound and tempo.

    A competitive product to the MT-36 was likely Yamaha PSS-150, which looks and sounds quite similar.

    Casio MT-200

    This keyboard of 1984 (concluded by Spanish sales brochure) is basically a longer and more professional older variant of Casio MT-36, with 8 nicely warm preset sounds, 6 rhythms, more controls and an additional stereo chorus.
    This instrument is the most complete and best sounding of the series. The demo was omitted, but fortunately also the sometimes annoying automatic fill-in.
     
    The most unique feature is the slot for the optional parallel port interface Casio PA-1, with that it could be connected to a computer.

    Also a black version was made (seen on eBay).

    main features:

  • 49 midsize keys
  • 2 built-in speakers (mono sound generator routed through a stereo chorus)
  • polyphony 8 notes (only 4 with chord or accompaniment)
  • 8 preset sounds {piano, elec. piano, organ, elec. organ, clarinet, oboe, vibraphone, strings}
  • 6 preset rhythms {rock, disco, swing, waltz, bossa nova, slow rock}
  • no (automatic) fill-in
  • separate chord & rhythm volume sliders
  • sustain switch
  • stereo chorus with on/off switch
  • single finger chord (has manual organ chord with rhythm off)
  • "bossa nova" rhythm has additional analogue conga drum
  • complex multi-chip hardware:
  • CPU= "NEC D8049C 557, 8349HX" (40 pin DIL , Intel MCS-48 with 2KB ROM)
  • sound IC= "HD43720, 3J 48" (54 pin SMD)
  • stereo chorus:  BBD= "MN3206" (8 pin DIL, 128 steps), clock= "MN3102" (8 pin DIL)
  • tuning knob
  • slot for computer interface Casio PA-1
  • jacks for power supply, headphones & line out

    		•

    eastereggs:

  • 2 additional rhythms addable.
  • auto-fill-in switch addable.

    • modifications:

  • polarity protection diode added, power supply jack polarity corrected.

    • notes:

    The outer case shape of this Casio instrument looks like their early keyboards (e.g. MT-60). Next to the tuning knob there is an unpunched hole for an additional jack, which is not supported by the PCB. Someone had soldered wires to the tuning potentiometer of my specimen - possibly to control or modulate the pitch externally.

    The main voice waveforms are bipolar multipulses and sound fairly ok. (IMO many Casio VL-1 waveforms sound more natural.) Worse is that the linear decay envelopes are too short. So even held 'piano' notes end already after 1s. Held notes of all other decaying preset sounds only last 0.5s. The sustain switch adds 0.5s sustain after key release (else notes stop immediately), but do not prologue held notes of decaying sounds. The 'vibraphone' has sustain always on and ignores that switch. Trilled keys produce a nice phasing and volume increase effect by occupying multiple polyphony channels. Interesting for playing is that the OBS preset sound buttons can also be pressed while keys are held down without stopping their notes. Like in MC-3, by rhythmically pressing them, many arpeggiator- like timbre changes can be created, thus this button field can be considered a realtime sound control, and unlike in many other digital instruments, the button field responds almost immediately without delay (which however causes some pop noises).

    The stereo chorus adds a 6Hz chorus vibrato to the main and chord voice when enabled. But even when switched off, it still slowly pans the sound left and right with about 0.5Hz. Unlike my first expectation, there is no fingered chord mode in this instrument. But at least there is a manual organ chord mode with rhythm off (made from multipulse chord + dull bass voice with a little sustain).

    Unlike MT-36 the "bossa nova" rhythm employs an additional analogue conga drum instead of the snare, and the base drum knocks louder (possibly by better speakers). The percussion also sounds a bit duller, which makes the grainy digital hihats less spectacular. Also the automatic fill-in of the MT-36 is missing, which makes the accompaniment patterns simpler but more versatile.

    To the right it has a screwed lid where the parallel port interface PA-1 can be inserted and even screwed on at the case holes. This ultra-rare interface has a Centronics printer plug at its side and was intended as a MIDI predecessor. I never heard of any other Casio instrument supporting it. There is a switch on the interface that (as far I remember) stops rhythm when turned on without a computer. According to MT-200 service manual, the PA-1 supports data transfer only one way to play music programmed on a "personal computer". I.e. it was only like midi-in and can not be used as a master keyboard for e.g. entering music into sequencer software. This is a bit disappointing, seeing that the (otherwise not cheaply built) MT-200 of all used one of the weakest polyphonic Casio sound ICs. If Casio would have used a programmable synth chip like in MT-65, in 1984 this could have been a game changer. AFAIK the only computer that used the MT-200 to play music was the fairly big and expensive Casio FP-1100.

    question: Does anybody know more about the Casio PA-1 interface? Which other computers could use it? Has anybody still software for it? The only other thing with "PA-" in its name was the later released toy keyboard Casio PA-31, which had nothing to do with it. Casio also first released the TA-1 tape storage interface and later a TA-10 toy keyboard - did they do this with all their interface names??
     

    circuit bending details

    The Casio MT-200 is based on the CPU "NEC D8049C 557" (clocked @ 4.96 MHz) with sound IC "Hitachi HD43720" and semi-analogue percussion. Casio MT-90 is the same, but lacks the computer port and a few related discrete components, despite the PCB still has empty solder holes and traces for it.
    This hardware has strong similarities with CT-102, thus for details see there. The main difference is that it is not crystal clocked and has auto-power-off, and of course the CPU has different software. But compared with CT-102 and MT-36 this is the most complex instrument of the series.

    That is to say, there is a large analogue stereo chorus section based on BBD ICs. Even in "off" position it is not off but only switched to a slower and weaker mode. In MT-200 and CT-102 the unused CPU pin 38 pulls lo during preset sounds {vibraphone, elec. organ, strings} and was likely originally intended as an automatic control for this (or a vibrato circuit). Despite MT-200 has only a manual slide switch for its stereo chorus, a yellow cable from there goes to one side of an unsoldered wire bridge that was apparently originally planned by Casio to enable it (or switch it to fast mode) only during these 3 sounds. The given slide switch was instead likely planned for automatic fill-in, which exists as an easteregg.

    The percussion in 'bossa nova' rhythm triggers an additional analogue conga through CPU pin 23.

    computer port

    According to MT-200 service manual, the PA-1 is a Centronics interface with data transfer only one way to play music programmed on a "personal computer". I.e. it was only like midi-in and could not be used as a master keyboard for e.g. entering music into a sequencer software. Disappointing is that the MT-200 of all had one of the weakest polyphonic Casio sound ICs. Casio should have used a versatile programmable synth IC like D931C to make this into an exciting product.
    The keyboard matrix is multiplexed additionally with a computer port that could be connected with the parallel port interface Casio PA-1 as kind of midi. Inside the PA-1 are 7 "74LS" logic ICs, diodes and resistors. CPU pin 8 goes to the IF1 foil cable of the computer port PCB (which contains 2x "74LS367A" and a "74LS00"). My MT-200 (PCB "M484-MAIM") does nothing with that cable unplugged, because this simultaneously disables the tristate drivers to all keyboard matrix ins (IF1 pin 17). I haven't investigated the port further, but it is all about multiplexing matrix lines. Possibly also the sound IC can be externally accessed from here, because matrix ins are connected with its data bus. My MT-90 has a slightly different PCB ("M481-MA1M", many wire bridges omitted or replaced with resistors) and of course runs without computer port PCB.

    In the service manual is a description of the parallel port protocol with timing chart. (/STROBE lo pulse needs to be 0.5..1uS. /RD lo pulse needs to be >300ms. /ACKNLG lo pulse needs to be >7us.)

    1. Personal computer confirms that the acknoledge signal /ACKNLG from PA-1 is "H" level and puts data on the data bus.
    2. Personal computer generates /STROBE signal which informs PA-1 that the data bus is carrying a data.
    3. From /STROBE signal, PA-1 generates BUSY and /INT signal.
    4. Personal computer receives BUSY signal.
    5. Receiving /INT signal, MT-200's CPU halts functioning to get ready to receive the data.
    6. MT-200 drops /RD signal to read the data. At the dropping edge of /RD, BUSY and /INT signals are reset.
    7. After reading the data, MT-200 raises signal /RD and at the rising edge of /RD, signal /ACKNLG is sent to the personal computer and the computer confirms that MT-200 has received the data.
    8. Data transfer is complete.
    The ROM contents of the MT-200 CPU strongly differs from MT-36, not least because it had to support the computer interface, so it may be that there was not enough rom space left to include the demo.

    keyboard matrix

    This keyboard matrix was originally examined by me, based on the service manual of Casio CT-102, and later corrected by that of MT-200 (which has different software). Unlike other models of this hardware families, the matrix outputs here are not inverted, but instead the matrix inputs to the CPU are switched through 2 tristate drivers TC40H367P and apparently multiplexed with computer port data. The matrix inputs of CPU pins 12..16 are also multiplexed with the sound IC data bus and thus may make strange sounds when fed with wrong signal timing.
     
    (12) KI1
    (13) KI2
    (14) KI3
    (15) KI4
    (16) KI5
    (17) KI6
    (18) KI7
    (19) KI8
     
    CPU pin
    in 1
    in 2
    in 3
    in 4
    in 5
    in 6
    in 7
    in 8
    in / out
     
    o
    C2
    o
    C#2
    o
    D2
    o
    D#2
    o
    E2
    o
    F2
    O.
    piano
    R.
    rock
    out 1
    27 KC1
    o
    F#2
    o
    G2
    o
    G#2
    o
    A2
    o
    A#2
    o
    B2
    O.
    elec. piano
     R.
    disco
    out 2
    28 KC2
    o
    C3
    o
    C#3
    o
    D3
    o
    D#3
    o
    E3
    o
    F3
    O.
    organ
    R.
    swing
    out 3
    29 KC3
    o
    F#3
    o
    G3
    o
    G#3
    o
    A3
    o
    A#3
    o
    B3
    O.
    oboe
    R.
    waltz
    out 4
    30 KC4
    o
    C4
    o
    C#4
    o
    D4
    o
    D#4
    o
    E4
    o
    F4
    O.
    clarinet
     R.
    bossa nova
    out 5
    31 KC5
    o
    F#4
    o
    G4
    o
    G#4
    o
    A4
    o
    A#4
    o
    B4
    O.
    vibraphone
    R.
    slow rock
    out 6
    32 KC6
    o
    C5
    o
    C#5
    o
    D5
    o
    D#5
    o
    E5
    o
    F5
     O.
    strings
     R.
    beguine?
    out 7
    33 KC7
     o
    F#5
    o
    G5
    o
    G#5
    o
    A5
    o
    A#5
    o
    B5
     O.
    elec. organ
     R.
    tango?
    out 8
    34 KC8
    o
    C6
    sustain
    C.
    single finger
    power off
    R.
    synchro
    R.
    start/stop
    R.
    auto-fill-in
    Comp
    out 9
    35 KC9

    The input lines are active-low, i.e. react on GND. Any functions can be triggered by a non- locking switch in series to a diode from one "in" to one "out" pin.
     

    legend:
    "o"
    		 = keyboard key
    underlined
    		 = function needs locking switch (i.e. stays active only so long the switch is closed)
    R.
    		 = preset rhythm
    O.
    		 = preset sound ('orchestra')
    C.
    		 = chord
    orange
    background     		 = easteregg (unconnected feature)

    The rhythm naming in MT-200 service manuals is wrong (column KI8 = {Rock, Swing, Bossa Nova, Waltz, Bossa Nova, Slow Rock, "", "", Comp} ) and its buttons only have numbers in the wiring plan, so possibly software wasn't finished when schematics was made. Unlike my expectation I did neither find a fingered chord mode nor unused vibrato output (measured CPU pins). The matrix place KI8->KC9 labelled "Comp" stops rhythm and has likely to do with the PA-1 computer interface.
     

    connector KY1

    pin  
    1 KC1
    2 KI1
    3 KI2
    4 KI3
    5 KI4
    6 KI5
    7 KI6
    8 KC2
    9 KC3
    10 KC4
    11 KC5
    12 KC6
    13 KC7
    14 KC8
    15 KC9

    connector CN1

    pin  
    0 BBDS
    1 KC9
    2 KC8
    3 KC7
    4 KC6
    5 KC5
    6 KC4
    7 KC3
    8 KC2
    9 KI6
    10 KI5
    11 KI3
    12 KI2
    13 KC1
    14 KI8
    15 KI7
    16 SCH
    17 TYR1
    18 TYR2
    19 TL
    20 VDD
    21 GND
    		  Because the matrix inputs are routed through tristate drivers, they were a little difficult to find. Bypassing these drivers (connecting directly to CPU pins) does not work. But they are also at 2 foil cables (pins numbered right to left) at the top left of the PCB. Thus in the following I refer to matrix pin names instead of CPU pin numbers. Even in schematics there is no pinout but a mess of individual pins in random order.

    • more preset rhythms
      Wire each a button through a diode at KI8->KC7 and KI8->KC8 for 2 additional preset rhythms ('beguine' and 'tango'?).
       
    • auto-fill-in
      Wire a locking switch through a diode at KI7->KC9 to enable automatic fill-in. Like in Casio MT-36, this will insert a fill-in every 4th bar of the rhythms. These also make additional use of the analogue conga, that outside 'bossa nova' stays mute. The fill-in patterns differ, and particularly in the unused rhythms at KC7 and KC8 sound a little broken, so these 2 may be data junk instead of actual patterns. Unfortunately there is no support for a manual fill-in button.

    Casio MT-90

    This was a later re-release(?) of the Casio MT-200 in brown without PA-1 interface slot. It still has empty PCB holes for components to connect the omitted slot PCB (my MT-200 won't run without). The CPU is "NEC D8049C 557, 8531B7" with sound IC "HD43720, 6A 13". (Hardware description see MT-200.)

    The German retail price in a Casio prospect of 1985 was 449DM.

    modifications:

    polarity protection diode added, power supply jack polarity corrected.

    Casio CT-102

    The CT-102 of 1985 (service manual date) was Casio's simplest fullsize beginners keyboard with accompaniment. Technically this is mostly a software variant of Casio MT-36, but behaviour resembles the more professional Casio MT-200, so it has single finger chord mode with rhythm off and no automatic fill-in.

    The CT-102 was also released in black. The German retail price in a Casio prospect of 1985 was 499DM.

    different main features:

    eastereggs:

    modifications:

    notes:

    By case shape, this keyboard would perfectly fit into the Casio CT-3x0 series; its different model number likely should indicate an even lower grade model with less features (e.g. no fingered chord). The speaker has nicely warm sound with enough bass, but sounds a little dull. I bought this one only because the service manual showed a different software number than related models, which was it worth and turned out to be interesting. The design concept of the CT-102 was likely inspired by the 4 years older Yamaha PS-10 (fullsize PS-2), although the technology is more digital and software controlled.
     

    circuit bending details

    The Casio CT-102 is based on the CPU "Toshiba TMP8049P, 3497" (crystal clocked @ 4.96 MHz) with sound IC "Hitachi HD43720" and semi-analogue percussion. It is closely related to Casio MT-36 and MT-200 (those have different software numbers); also here the CPU is an Intel MCS-48 variant with 2KB ROM (I dumped it).
    Schematics of an unknown Chinese variant CH-100 (mentioned in Chinese book "Electronic Keyboard Principle & Maintenance" (ISBN 7-03-003804-5/TN-153) - thanks Traktor for info) look the same but lack discrete parts section for accompaniment and single finger chord switch, which makes me conclude that the CH-100 has none.

    sound generator

    This sound hardware was apparently Casio's first cheap polyphonic sound ic with integrated DAC, chord and percussion generator. The main voice generator is obviously a polyphonic successor of the great multipulse squarewave sound engine of Casio VL-1, but unlike there, the blocky waveforms are bipolar, i.e. made from 3 levels {-1, 0, +1} (which IMO did not improve timbre quality). So the sound IC has 2 DAC outputs for a main and a sub waveform, those are mixed through resistors in a ratio of 1:64. With held monophonic notes the main waveform looks like a normal multipulse, while the sub waveform has 3 levels {-1, 0, +1} and looks like the tone. During falling volume envelope, the equidistant "0" sections of the main waveform rapidly move many times linearly up and down while the sub waveform amplitude slowly shrinks. I am not sure if these observations (seen on analogue oscilloscope) are only artifacts of sending upper and lower waveform bits to a separate DAC, or if main and sub waveform indeed get computed this way by 2 independent generators to combine into the envelope. Likely the main waveform only scales the envelope; in most preset sounds it is plain squarewave, but in 'elec. piano' and 'clarinet' it is a multipulse, so it may be that this is a very crude kind of phase distortion (FM) mechanism involving analogue multiplication of both components (main waveform has 2 diodes in series to GND, which may intend nonlinear behaviour), although it does not vary modulation depth to change timbre. (It would be interesting to build a more programmable version of this, to examine what else it can do.)

    The unused 11-bit DAC output port makes me conclude that for 8 note polyphony (3 bits) each polyphony channel including envelope has 8 bit. The sub waveform of one note is up to 5 steps high (seen on analogue scope), hence the sub waveform is 3-bit while the main waveform has likely 63 steps and thus 5-bit. In preset sounds 'piano' and 'vibraphone' the sound ic pulls pin 11 lo to enable a discrete external filter that makes them duller and adds a little resonance.
     
    preset sound sub waveform main waveform envelope
    piano 11111100 11111100 decay 1s
    elec. piano 1--01-00 011X01XX decay 0.5s
    organ 1---1-00 11111100 hold + slow attack 
    oboe 1-----10 11111110 hold + slow attack
    clarinet 11-100-0 11110010 hold
    vibraphone 1---0--- X111X111 decay 0.5s + always sustain
    strings 100----- 10011111 hold + slow attack
    elec. organ 1-101--0 11101110 hold
    bass & chord 11110010   (capacitor sustain)
    		The complete waveforms on analogue oscilloscope look very distorted by capacitors, thus the bipolar multipulse patterns were hard to identify, but they seem to be indeed identical with their own "sub" waveform, which shape is better visible. The "-" indicates the intermediate level (center line) between 0 and 1.

    The "main" waveforms here are only an approximation. Their "X" sections move rapidly. The "0" section amplitude moves with envelope. But these don't strongly change the complete waveform anyway but mainly affect envelope.

    The volume envelopes are linear with very few internal parameters. Unfortunately they decay too fast. Sustain decays 0.5s after key release.

    On the PCB is a trimmer VR2 "BIT COMP ADJ" for main voice bit compensation (tweak low DAC bits) that adds a positive or negative version of the sub waveform (from 2 different pins) to the sum. Adjust the trimmer to minimize distortion during decay of 'vibraphone'. Despite this effort, the resulting waveform has still strange edge glitches and the linear volume envelopes are strangely jagged (like modulated with falling sawwave) and wobble at the end (causing a weak dull end click).

    The bass and chord voices are normal multipulses output through 4 separate pins with corresponding separate envelope trigger outs and capacitors. Despite these do not use the melody voice DAC, internally they occupy 4 of the main voice channels.

    The semi-analogue percussion generator of the sound ic outputs on separate pins 2 different hiss noises (semi-metallic and snare) and envelope triggers for {cymbal+hihat, base, snare} those apparently choke (pull down) the noise outputs through capacitors and resistors to shapen it. Despite coarse digital waveforms and the envelopes look truncated (end too soon), these are not typical blip percussion but sounds fairly analogue, which is likely result of the capacitor envelope without zipper noise.

    Shorting data bus lines buzzes and plays some note and percussion mess, but the synthesis engine does nothing spectacular but only selects random preset sounds. This hints that (like in early digital Yamaha keyboards) the sound IC does not receive synthesis parameters but only preset sound numbers from the CPU and hence can not be freely programmed.

    The trimmer VR1 "GAIN ADJ" is not even explained in the service manual text, but according to schematics it controls the main voice level at the transistor T2 output (collector) of the melody circuit entering the filter block. So this may be a preset volume control for it.

    keyboard matrix

    This keyboard matrix is based on the original service manual of Casio CT-102. The matrix outputs from the CPU are routed through inverters (2x "TC4049BP").
     
    12 KI1
    13 KI2
    14 KI3
    15 KI4
    16 KI5
    17 KI6
    18 KI7
    19 KI8
     
    CPU pin
    in 1
    in 2
    in 3
    in 4
    in 5
    in 6
    in 7
    in 8
    in / out
     
    o
    C1
    o
    C#1
    o
    D1
    o
    D#1
    o
    E1
    o
    F1
    O.
    piano
    R.
    rock
    out 1
    /27 KC1
    o
    F#1
    o
    G1
    o
    G#1
    o
    A1
    o
    A#1
    o
    B1
    O.
    elec. piano
     R.
    disco
    out 2
    /28 KC2
    o
    C2
    o
    C#2
    o
    D2
    o
    D#2
    o
    E2
    o
    F2
    O.
    organ
    R.
    swing
    out 3
    /29 KC3
    o
    F#2
    o
    G2
    o
    G#2
    o
    A2
    o
    A#2
    o
    B2
    O.
    oboe
    R.
    waltz
    out 4
    /30 KC4
    o
    C3
    o
    C#3
    o
    D3
    o
    D#3
    o
    E3
    o
    F3
    O.
    clarinet
     R.
    bossa nova
    out 5
    /31 KC5
    o
    F#3
    o
    G3
    o
    G#3
    o
    A3
    o
    A#3
    o
    B3
    O.
    vibraphone
    R.
    slow rock
    out 6
    /32 KC6
    o
    C4
    o
    C#4
    o
    D4
    o
    D#4
    o
    E4
    o
    F4
     O.
    strings
     R.
    rock
    out 7
    /33 KC7
     o
    F#4
    o
    G4
    o
    G#4
    o
    A4
    o
    A#4
    o
    B4
     O.
    elec. organ
     R.
    rock
    out 8
    /34 KC8
    o
    C5
    -
    C.
    single finger
    -
     R.
    synchro
    -
    sustain
    R.
    start/stop
    out 9
    /35 KC9

    The input lines are active-low, i.e. react on GND. Any functions can be triggered by a non- locking switch in series to a diode from one "in" to one "out" pin.

    The matrix inputs of CPU pins 12..16 are multiplexed with the sound IC data bus and thus may make strange sounds when fed with wrong signal timing.
     

    legend:
    "o"
    		 = keyboard key
    underlined
    		 = function needs locking switch (i.e. stays active only so long the switch is closed)
    R.
    		 = preset rhythm
    O.
    		 = preset sound ('orchestra')
    C.
    		 = chord
    orange
    background     		 = easteregg (unconnected feature)
    grey
    background    		 = unconnected doublet

    Unlike my expectation I did neither find a fingered chord mode nor unused vibrato output (measured CPU pins). Despite the given slide switches in CT-102, preset sounds and rhythms need no locking switch.
     

    connector JA

    pin  
    1 KC1
    2 KI1
    3 KI2
    4 KI3
    5 KI4
    6 KI5
    7 KI6
    8 KC2
    9 KC3
    10 KC4
    11 KC5
    12 KC6
    13 KC7
    14 KC8
    15 KC9

    connector JB

    pin  
    1 KI3
    2 KI8
    3 KC1
    4 KC2
    5 KC3
    6 KC4
    7 KC5
    8 KC6
    9 KC9
    10 KI7
    		  Because the matrix outputs are routed through inverters, they are a little difficult to find. But they are also at 2 foil cables "JA" and "JB" (pins numbered right to left) at the top left of the PCB. Thus in the following I refer to matrix pin names instead of CPU pin numbers.

    • more preset sounds
      Wire each a button through a diode at KI7->KC7 and KI7->KC8 for additional preset sounds 'strings' and 'elec. organ'. (Set the preset sound slider into an intermediate position to use them.)
    • more preset rhythms
      Wire each a button through a diode at KI8->KC2 and KI8->KC5 for additional preset rhythms 'disco' and 'bossa nova'. (Set the preset rhythm slider into an intermediate position to use them.)
      In CT-102 and CH-100 schematics the CPU pin 36 has a 22k pullup resistor and is pulled lo by a jumper "J-A" that is marked "ONLY MX-141". This seems to be a model select feature (possibly for the Chinese CH-100); when disconnected, the rhythm patterns change and accompaniment stays mute (likely by omitted accompaniment patterns in rom); chord voice with rhythm off still works. Install a switch instead of the wire bridge if you want. The rhythms {rock, disco, swing, waltz, bossa nova, slow rock} turn into {march, march, waltz, slow rock, march, 4 beat} (also 'rock' doublets become march). Pulling pin 36 hi (switch open) takes effect immediately; pulling it lo (switch closed) does nothing until a rhythm is selected.
      In CH-100 keyboard matrix function names are Chinese characters and the 4 rhythms (same matrix places like in CT-102) are named {2/4, 3/4, 6/8, 4/4}. The '3/4' at KC3 is likely 'waltz', which hints that CH-100 lacks this jumper.
    • synchro start
      Wire a button through a diode at KI5->KC9 for synchro start.

    pinout TMP-8049P-3437, TMP-8049P-3497, D8049C 557

    The "NEC D8049C 557" (and variant "D8749H-A") is the CPU of Casio MT-200 & MT-90.
    The "Toshiba TMP8049P 3437" is the CPU of Casio MT-35 & MT-36.
    The "Toshiba TMP8049P 3497" is the CPU of Casio CT-102, CH-100 & CH-102.

    Technically the "TMP8049P-xxx" (aka "D8049C xxx", 40 pin DIL) is a generic microcontroller of the well documented Intel MCS-48 family, so everything it does is entirely controlled by software of its internal 2k ROM. But all 3 software versions were designed to be almost pin compatible, so I describe them together. They all poll the keyboard matrix and control a sound IC HD43720.
     
    software number hardware class notes & features
    557 MT-200 conga trigger out, supports parallel port interface PA-1
    3437 MT-36 demo song, no manual chord mode, no sustain, always auto-fill-in
    3497 CT-102 no APO

    I dumped the internal rom of these. The hex code of MT-200 and CT-102 have some identical sections, while MT-36 strongly differs, which makes sense because the behaviour of CT-102 has more similarities with MT-200.

    In MT-200 service manual is a note: "The first a few lot of MT-200 employ D8749H-A instead of µPD8049C-557. When D8749H-A is replaced with µPD8049C-557, it is neccessary to change the coil and the capacitors in the oscillator circuit." (The coil changes from L20-705 to L40-705, both caps from 10pF to 5pF. It is unknown which one ran at 7 Mhz as indicated in CPU pinout.)

    This pinout was based on software number "3497" from CT-102 and later MT-200 service manual, my own examination of both other CPUs and Intel MCS-48 datasheets.
     
    pin name purpose
    1 TO MT-36: (wired to +Vs) | MT-200: (wired to ground) | CT-102: clock out (1.65 MHz to sound ic)
    2 XTAL clock in (CT-102: 4.96 MHz | MT-200: 7 MHz)
    3 XTAL2 clock in
    4 /RESET reset
    5 /SS halt | MT-36, MT-200: APO in (wired to pin 36) | CT-102: (wired to pin 6)
    6 /INT interrupt in (resistor to +Vs) | MT-200: PA-1 interface interrupt
    7 EA (wired to ground)
    8 /RD MT-200: (PA-1 interface read, to IF1 pin 15)
    9 /PSEN (not used)
    10 /WR write (sound ic pin 46)
    11 ALE clock div out (not used)
    12 DB0 key matrix in (in MT-200 muxed with computer port) | data bus (sound ic pin 53)
    13 DB1 key matrix in (in MT-200 muxed with computer port) | data bus (sound ic pin 52)
    14 DB2 key matrix in (in MT-200 muxed with computer port) | data bus (sound ic pin 43)
    15 DB3 key matrix in (in MT-200 muxed with computer port) | data bus (sound ic pin 42)
    16 DB4 key matrix in (in MT-200 muxed with computer port) | data bus (sound ic pin 41)
    17 DB5 key matrix in (in MT-200 muxed with computer port)
    18 DB6 key matrix in (in MT-200 muxed with computer port)
    19 DB7 key matrix in (in MT-200 muxed with computer port)
    20 Vss ground 0V
    21 P20 chip select out (sound ic pin 45)
    22 P21 handshake out (sounc ic pin 44)
    23 P22 MT-36: reset out (sound ic pin 50) | MT-200: percussion conga trigger /out
    24 P23 MT-200, CT-102: reset out (sound ic pin 50)
    25 PROG (not used)
    26 +VDD supply voltage +5V
    27 P10 key matrix out (in MT-36, CT-102 inverted)
    28 P11 key matrix out (in MT-36, CT-102 inverted)
    29 P12 key matrix out (in MT-36, CT-102 inverted)
    30 P13 key matrix out (in MT-36, CT-102 inverted)
    31 P14 key matrix out (in MT-36, CT-102 inverted)
    32 P16 key matrix out (in MT-36, CT-102 inverted)
    33 P17 key matrix out (in MT-36, CT-102 inverted)
    34 P15 key matrix out (in MT-36, CT-102 inverted)
    35 P24 key matrix out (in MT-36, CT-102 inverted)
    36 P25 MT-36, MT-200: APO out (to pin 5) | CT-102: model select (wired to ground = CT-102)
    37 P26 MT-200, CT-102: tempo led /out (CT-102: not used)
    38 P27 MT-200, CT-102: chorus control /out (CT-102: not used)
    39 T1 accompaniment tempo clock in
    40 VCC supply voltage +5V

    Inserting the MT-36 or MT-200 CPU into CT-102 does nothing (stays mute) because CT-102 is crystal clocked and depends on sound IC clock from CPU pin 1, which is produced externally in other models.

    Inserting  the CT-102 CPU into MT-36 works (chord switch activates manual chord), but 'rhythm start/stop' and 'demo' switch don't work due to changed matrix layout. Once started through matrix pins, rhythm works correctly (preset rhythm buttons, tempo), but because pin 36 is hi (model select = CH-100 in this CPU), there is no accompaniment.

    Inserting  the CT-102 CPU into MT-200 makes cacophonic note cluster mess on keys and nothing works (any preset rhythm button behaves like 'rhythm start/stop', other buttons do nothing) because its key matrix out pins are not inverted and all matrix inputs switched through 2 tristate drivers TC40H367P and multiplexed with computer port data.

    The tempo potentiometer adjusts an external oscillator (made from inverter IC TC40H004P and a 47nF cap), which frequency is fed into pin 39.

    Pin 5 is halt (single step input). Pin 8 (output strobe) has 4V with lo spikes. Pin 9 and 25 are hi (4V). Pin 11 (address latch enable) looks like a clock divider out. These may be normal behaviour of the MCS-48 and not related to hidden features. 

    In MT-36 and MT-200 pin 36 is APO out; it pulls lo to activate auto-power-off (standby mode). Interesting is how pin 36 is additionally wired to pin 5 (halt) to stop the CPU during standby.

    In CT-102 and CH-100 schematics pin 36 has a 22k pullup resistor and can be pulled lo by a jumper wire "J-A" that is marked "ONLY MX-141". The jumper exists in my CT-102; removal changes rhythm patterns and mutes accompaniment, so it was likely a model select feature.

    In CT-102 and MT-200 the unused pin 38 pulls lo during preset sounds {vibraphone, elec. organ, strings} and was likely originally intended as an automatic control for an external stereo chorus or vibrato circuit. Despite MT-200 has only a manual slide switch for its stereo chorus, a yellow cable from there goes to one side of an unsoldered wire bridge that was apparently originally planned to enable it (or switch it to fast mode) only during these 3 sounds. The given slide switch was instead likely planned for automatic fill-in (an unused easteregg).

    In MT-200 pin 8 goes to the IF1 foil cable of the computer port PCB. The MT-200 does nothing with that cable unplugged, because this disables the tristate drivers to all keyboard matrix ins (IF1 pin 17). I haven't investigated the port further, but it is all about multiplexing matrix lines. Possibly also the sound IC can be externally accessed from here, because matrix ins are connected with its data bus.

    In MT-200 pin 23 triggers an analogue conga, that is only used by 'bossa nova' and the automatic fill-in easteregg.

    pinout HD43720

    The Music LSI "Hitachi HD43720" (54 pin SMD, pins count anticlockwise from below the left stub pin) is the squarewave sound IC of various early Casio beginners keyboards. It contains 8 polyphony channels for melody voice (4 of these can be re-routed as chord & bass voice) with linear envelope. Additionally there is a percussion generator with waveform outs for {base, snare, cymbal+hihat} and corresponding trigger pins for external analogue envelope circuits. Also the 4 separate chord & bass outs have each an envelope trigger pin. As a real sound IC it needs to be controlled by an external CPU through a data bus. The integrated DAC the integrated DAC outputs its lower bits (at increased level) only on a separate pin; also the highest bit is separately output in normal and inverted. All these have to be combined through an external voltage divider (small resistor network with ratio 1:64), which was likely done to reduce noise. The only 11 DAC bits also have separate output pins (not used in any instruments I know).

    Each waveform is made from bipolar multipulse squarewave (8 steps long) and a simple volume envelope that does not change with note pitch. Each step can have only the height {-1, 0, +1}, i.e. protrude fully up, fully down or be zero. The linear envelope and low bit resolution make it sound rather artificial, but the unusual sonorous waveforms are unique and the high internal clock rate (1.65 MHz) prevents cold aliasing noise. Unlike the more advanced D77xG there is no spread scale, i.e. holding the same notes in different octave (except the highest note) causes no phasing (but phase changes among trilled decaying notes, thus there are no octave dividers involved).

    It is unknown if synthesis parameters are send by the host CPU to the sound IC (like in D931C), or if it only can select 8 preset sounds from an internal rom (like done in early Yamaha keyboards). The fact that all known instruments with HD43720 contain the same preset sounds suggests the latter.

    This pinout is based on the Casio CT-102 service manual and my own examination.

    caution: This IC uses "negative logic", i.e. technically +5V is its GND while 0V is its -5V supply voltage. So the voltages are not was the pin names suggest. I use the positive voltage naming convention (from 0V to +5V, not -5V to 0V). Apparently all "O#" pins are outputs, "I#" are inputs and "IO#" can be both. "DB#" are data bus. "T#" are test pins.
     
    pin name purpose
    1 O4 chord envelope out
    2 O3 chord envelope out
    3 O2 chord envelope out
    4 O1 bass envelope out
    5 IO14 (not used)
    6 IO13 (not used)
    7 O18 hihat/cymbal select out
    8 O17 cymbal+hihat envelope trigger out
    9 O16 base envelope trigger out
    10 O15 snare envelope trigger out
    11 O19 melody filter control out
    12 O14 percussion white noise wave out
    13 O13 base wave out
    14 O12 snare wave out
    15 I4 (wired to +Vs)
    16 I5 (wired to +Vs)
    17 I6 (wired to +Vs)
    18 I7 (wired to +Vs)
    19 IO12 dac bit out (not used)
    20 IO11 dac bit out (not used)
    21 IO10 dac bit out (not used)
    22 IO9 dac bit out (not used)
    23 IO8 dac bit out (not used)
    24 O11 melody audio out (lower bits, weighted 1/64)
    25 O10 melody audio out (upper bits)
    26 VDAC analogue ground 0V
    27 GND supply voltage +Vs (+5V)
    -   (no pin)
    pin name purpose
    28 IO7 dac bit out (not used)
    29 IO6 dac bit out (not used)
    30 IO5 dac bit out (not used)
    31 NC  
    32 IO4 dac bit out (not used)
    33 IO3 dac bit out (not used)
    34 IO2 dac bit out (MSB, not used)
    35 IO1 bit compensation
    36 O9 bit compensation
    37 O8 bass wave out
    38 O7 chord wave out
    39 O6 chord wave out
    40 O5 chord wave out
    41 DB5 data bus
    42 DB4 data bus
    43 DB3 data bus
    44 I3 data handshake
    45 I2 chip select in
    46 I1 /write in
    47 T1 test (wired to +Vs)
    48 T2 test (wired to +Vs)
    49 T3 test (wired to +Vs)
    50 SCH reset
    51 OSC clock in (1.65 MHz)
    52 DB2 data bus
    53 DB1 data bus
    54 VDD ground 0V
    - (stub)  

    By pinout and behaviour, this sound IC is a close relative of the single chip keyboard CPU HD44140 (found in Casio PT-7, MT-11 etc.), however unlike there it doesn't seem to layer 2 waveforms with independent volume envelopes (like Consonant-Vowel synthesis) but has only 1 static waveform. By its very few sound parameters and integrated percussion, this was obviously Casio's competitor to the Yamaha DSG YM2163, although by more natural timbres and twice the polyphony it ranks a step higher.

    The service manual mentions that the data protocol transmits per note 3x 5-bit data, separated by a handshake ("data punctuation signal") on pin 44. Pin 8 switches an envelope capacitor to make the cymbal decay slower than the hihat.

    The shift register feedback noise at the "white noise" output pin 12 is not white but rather semi-metallic. It apparently gets shorted by external discrete components so long cymbal, hihat and snare are not sounding. The snare mixes it with an additional noise from pin 14.

    Like in HD44140 there are 11 unused DAC bit outputs. Pin 32 only shows pulses when minimum 2 notes sound, pin 33 when 3 notes sound, which makes me conclude that these are the MSB.

    Pin 6 in CT-102 outputs a frequency of about 90 kHz at a duty cycle 1:7 (i.e. spikes up); this pin name is missing in schematics and thus is a guess (concluded from others). Pin 5 looks like inverted pin 6 but triggers badly on my analogue scope, so there may be serial data embedded in the signal. In MT-36 they are hi; pulling them lo goes into standby mode (APO).

    Pins 47 to 49 in CT-102 & MT-200 are wired to +Vs, but in MT-36 they are open (hi). Pulling them lo stops notes and makes all kind of bizarre crash noises (hiss like an untuned old radio etc.); when released it works normal again (wrong triggered notes still sounding). It is hard to estimate what is going on here; perhaps they are JTAG pins those interconnect all memory cells as a shift register, because glitch noises have nothing common with the normal sound. Particularly pin 47 is very sensitive and triggers random sounds when touched with scope probe; e.g. low buzzing notes with bass waveform buzz out of the melody voice DAC.

    Also pins 15..18 in CT-102 & MT-200 are wired to +Vs, but in MT-36 they are open (hi) and apparently unused outputs (pulling low through 1k barely changes voltage).

    Chinese CT-102 variants were apparently CH-100 (lacks accompaniment hardware) and CH-102 (schematics seen in Chinese book "Electronic Keyboard Principle & Maintenance").
     

     removal of these screws voids warranty...    
    WarrantyVoid
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