[sdiy] x0x memories (TB-303, TR-606, TR-808)

[Colin f]

> D'oh... I just realized that the 16 LEDs show the pattern for 
> the selected 
> instrument immediately when the pattern starts, so of course 
> the data must 
> be cached to some extent... :-/

The key scanning routine, which runs every 1.8ms, reads the step key state
and pattern data in groups of 4, updates the pattern memory and outputs the
current data to the LED drivers. The 808 service manual goes into quite a
lot of detail about how this works.
The data is read from memory as it is strobed to the LEDs.
CPUs of the 808 kind will probably only have 2 or 3 internal registers, so
there'd be no space to cache a pattern.

Cheers,
Colin f