Yamaha CS80

Colin f wrote:
>  
>   
>> They use the same 
>> ring memory table in the GX-1 and key assigner of the CS 50/60/80.  
>> There is a somewhat cryptic explanation in the CS service 
>> guide, pages 
>> 11 to 19, describing the encoder for 4 voices.  JH references the 
>> service guide on his CS50 page,
>>     
>
> You'll find the GX1 KAS schematic here:
> http://www.sequentix.com/gx1/GX1-KAS.zip
>
> Are the separate assigner and octave chips used elsewhere ?
> Looks like they were combined into a single chip for the CS synths, with a
> matrix of keys rather than an input for every single key.
>   
  They integrated the octave and semitone into a sort of matrix; it 
would first sense the octaves of keys by setting the octave pins to 0V 
(a grey bit, not logic 1 or 0) and setting the note pins to logic "1" 
aka -6.5v.  IT would record the octaves found in a buffer.  Then it 
would *reverse* the sense of a key and set all the 1s (-6.5v) to 0s 
(+8.5v).  This would show which actual notes in each octave were 
active.  Then they pack up the 3-bit octave code and 4-bit note code for 
good old time-division multiplexing at the DAC.  Skew the clock, and you 
get the glissando/portamento.  What a weird encoder. :)

  I built a CS-KAS based on PICs a while ago.  It works, but I did not 
adopt their strange assign order and instead went with the two popular 
ones, "steal oldest note" and "steal least used note".  I need to finish 
that thing, it still needs the gliss/porta function to actually work.  
Never enough time...
>>   If you look closely you'll see the actual electrical 
>> operation of the 
>> key scanner is ternary, not binary, it uses both -6.5v to 0 and 0 to 
>> +8.5v to derive logic states.
>>     
>
> I'm sure that's not the case on the GX.
> It has a +6/-9v supply for the assigner and octave scanning chips, but that is just to limit the total supply voltage to 15v for the CMOS devices that are used for the de-mux etc.
>
>   
  Yes, this is a common Yamaha trick, though nothing beats the -12V 
logic of the GS1, with a -7V supply node for the 5-volt logic (the patch 
controller).  Gotta love that old PMOS technology... ;)

Crow
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