Hi Chip,
1) Probably it should be "NC" for "no connection". If you look at the
schematics of the "New Production" you can find this.
Maybe it has a meaning in another keyboard of this era. The same
key assigner (8049C-217) was used in the MONO/POLY and the first
generation Poly-61 ("old production").
2) I think things were not much faster those days. The MCU runs off a
6MHz resonator. Due to internal timing this is divided by 15 giving
a core frequency of 400kHz / 2.5usec. The timer is set to 640usec,
which matches your measurements (676usec). All the recurring stuff
(KBD/button scanning, voice CV output, etc.) is done within the
timer interrupt service routine. Due to different code in different
phases:
- slot 0..5 (voices)
- slot 6..7 (calibrating the antilog amplifier)
- slot 8 (kbd/button scanning plus other housekeeping)
slightly different times occur. The timer ISR itself does not take
that much time but the 4051 muxes are only updated at this rate.
There is a lot other code outside the timer running - it is pretty
much stuffed up to the last byte...
Have fun with your project!
Johannes
On 2013-02-08 19:06, chipaudette wrote:
> Hi All,
>
> I've started my project to add aftertouch and velocity functions to my Polysix. After studying the schematics and planning out the circuitry needed to implement these functions, I went ahead and ordered the new keybed.
>
> To implement the velocity portion, I need to know which Polysix voice goes with each key press. So, I'm pretty sure that I need to replace the built-in key assigner with my own key assigner...this will allow me to have total control over which key press goes with which voice. Since many of the MIDI kits for the polysix already do this, I'm thinking that I'm up to the task.
>
> I've started to probe all the signals generated by the Key Assigner microprocessor. I've documented my results on my blog (link below) to show graphs and timing values. I have some questions that you might know...
>
> http://synthhacker.blogspot.com/
>
> My questions for you all are:
>
> 1) What does the "MC" line do? I can't find where it links to anywhere.
>
> 2) Why are the voice periods so long (676 usec). If they just wanted to latch in the pitch CV into the S-H circuit, couldn't they have used a much shorter period? If they used a shorter period, wouldn't they be able to greatly increase the update rate?
>
> Thanks for your thoughts!
>
> Chip
>
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>
> ------------------------------------
>
> Yahoo! Groups Links
>
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>
>