Part 2 of the Casiotone M10 History, Test and Review!

[Chas]

I've completed and uploaded Part 2 of my Casiotone M10 video. Lots of information in it regarding this little keyboard, along with some surprises and revelations. Also more audio demos and "Fun Facts! too". Enjoy!
 

 

[pianokeyjoe]

I liked this review my friend! I went and saw your Jan 2021 video too. Wow, alot of work! I hope the channel takes off like you want it. Another 8bit guy in the making here!! We need more! Now like I commented on the video itself, the organ sound on the M10 is the pipe organ sound on the MT65 and it's variants. I was actually well pleased and surprised. The other sounds are also from the MT65. I am checking on the LSI version to see if this is electronically true, cause if it IS? Oh boy! The MT65 has 23 tones too of which 3 more need to be unlocked lol. This keeps getting better and better.

[CYBERYOGI =CO=Windler]

MT-65 uses a CPU with separate soundchip. The M10 has single-chip hardware (D77xG family).

 

The "NEC D77xG" (64 pin zigzag DIL) was Casio's first polyphonic keyboard CPU that was used until 1981(?). It contains a keyboard matrix decoder with 4 quick access memory settings for favourite preset sounds, those are normally selected through keyboard keys + select button, but this selection method can be also simulated by preset sound buttons connected through logic ICs (like in Casiotone 401; pulling pin 34 hi seems to mute the demo note). The sound generator is 8 note polyphonic with digital envelope and stair shaped waveforms those sound much like multipulse squarewave. The 14bit digital audio output is fed into an external resistor ladder DAC. Each sound is made from 2 layered subvoices with independent envelope, what Casio called "Consonant-Vowel-Synthesis". It can additionally select timbres through an external analogue filter circuit controlled through 8 digital switch outputs. 2 of these CPUs with different software number can be wired parallel (one polls the keyboard matrix while both read it) to produce more complex layered preset sounds (4 subvoices using 2 filters). The tone scale can be switched from normal chromatic to a slightly spread variant which produces a chorus effect when 2 layered ICs set it differently. Clock can be input at pin 37 and output from pin 35 (half speed) daisychained to another CPU, or pin 35 is used as input. Bizarre is that this special CPU contains an LCD display port that is not used in any Casio keyboard (nor would it make sense in LCD pocket calculators due to size and power consumption). The CPUs in my 201 run a little hot - possibly because the digital supply voltage has 5.2V instead of the expected 5V and the analogue supply voltage is even 6V. In Casiotone 202 both have only 5V.

 

The naming convention of this earliest Casio keyboard CPU family is horrible; instead of software numbers the main number increases without any logical structure. It may be that advancing the 2nd or 1st digit reflects envelope algorithm changes or size of internal memory, but it also may be simply derived from the release date. According to Robin Whittle, all these ICs seem to differ only in their preset sound set and subtle changes like whether they can do sound selection without playing a demo note. He later called the hardware family 'Series I', but I prefer 'D77xG' despite it contradicts the naming in later keyboards.
 

CPU number	hardware class	notes & features
D771G	Casiotone 201	layered with D772G
D772G	'' (cpu 2)
D773G	Casiotone 301, 401, M-10
D775G	MT-30, MT-40
D776G	Casiotone 403 (old)	later version has D990G
D788G	Casiotone 202	layered with D789G
D789G	'' (cpu 2)
D990G	MT-60, Casiotone 403 (new)	bugfixed D776G?

 

Like with most special Casio ICs there are no datasheets online, but with modern NEC ICs the prefix D77 is  used e.g. for 16 bit fixed point DSPs, D78 for generic microcontrollers (like D7811G) and D990 can be digital codecs, so it even may be that these CPUs are (e.g. by Allen's patent lawsuit) internally completely different and only share their pinout. But the very similar sound and behaviour of affected keyboards make this unlikely. Modern NEC IC types have a huge variety of variants and their numbers are longer, so it may be that in 1980 the naming convention did not exist yet and diversified during the following few years which resulted in changing prefix numbers within one family.