It means Custom wavetable sound generator logic on Bubble System.
It's wavetable select and volume is controlled by single AY-3-8910 IO for both channels, Another AY-3-8910 IO is used for reading sound status.
Schematics: http://pdf.textfiles.com/manuals/ARCADE/K-R/Nemesis%20[Schematics]%20[English].pdf (Nemesis, derivative of Bubble system)
Bubble System 2 channel Wavetable sound generator logic is configuration with K005289, 4 bit PROM and DAC.
K005289 controls pitch and 5 bit address generator per channel, Waveform select and Volume control is tied to AY-3-8910 ports. (each port for per channels)
these configuration is better known as K005289, the part of logic.
furnace emulates this configurations as single system, waveform format is 15 level and 32 width.
cam900