In 99. Parallel bus I used the simple case of 6 bits per word and it's pretty simple.

In 16. Run Length Limitation, reduced I used a 8-bit word and I got the circuit wrong. I just realised I needed to invert the input data before the popcount, so it could work correctly on a parallel bus and have 4 or less bits set at one time.

The new circuit is there :

Add the NRZ/NRZI flipflops and you got a TMPI (Transistion-Minimised Parallel Interface).

The updated version of the 6-bit circuit is there:

The source code for the 6-bit and 8-bit versions are available in parpop_20251123.tgz