[sdiy] Polyphonic keyboard scanner

[Ingo Debus]

Am 31.07.2009 um 19:24 schrieb Jerry Gray-Eskue:

> That being said the only chance you have of implementing something  
> this
> complicated in a small number of chips without a processors is a  
> very old
> school trick, an EPROM that takes all the keys as on or off (1 or  
> 0) as the
> address and at that memory location has the proper binary settings  
> for the
> rest of the system,

Ugh.
How big an EPROM (or how small a keyboard) would you want to use? A  
27C160 has 21 address lines (in 8 bit mode), that's less than two  
octaves. You couls cascade EPROMS for more keys, but every additional  
key doubles the number of EPROMS.
Also, you need pitch and gate information for each synth voice, thus  
(at least) one eight bit EPROM per synth voice: 7 bit for pitch and  
one for gate. Ok, for a small keyboard you'd only need 5 bits for  
pitch, thus you could stuff five voices into four 8-bit-EPROMs or two  
16-bit-EPROMs.

Or did I get your idea completely wrong?

Another point, David asked for a solution without programmable logic  
chips (what does that P in EPROM again stand for?). While the EPROMs  
don't contain a computer program in the strict sense, you'd surely  
need to write a program of some sorts to generate that huge amount of  
data.

Ingo