It seems I'm on my own with this one...
I guess most people don't write multiplexing routines for nixie tubes anymore.
With an interrupt rate of 6.4kHz....
I have
156us blank, 2.97ms Pattern A, 156us blank, 2.97ms Pattern B which I call a 'frame'
Grouping into groups of five frames I change Pattern A and Pattern B to be ON for 0,1,2,3,4 or 5 frames to give a form of dimming.
When fading up/down i.e. changing ON frames from 0/5, 1/5, 2/5, 3/5, 4/5 and 5/5 with a fade increment every 30 frames...
I seem to get about the right effect, the flicker is quite noticeable when dimming up one cathode at the same time as dimming down another, when I dim up one and then fade out the other it seems better.
I have a few effects coded now... scroll, slot machine, fade digits, scroll-back (when displaying '0' after '9', instead display 9876543210 in rapid succession).
Does 6.4kHz sound reasonable for a 2-way multiplex?