I posted an answer to the question MSX's primary and secondary slots but while researching some references in the msx.org wiki to ensure my answer was accurate, I found some discrepancies between my recollection and the information I found.
There was an incompatibility between the way the Hotbit (HB-8000) and the Gradiente Expert mapped slots into each of the four 16kb memory pages. This I remember vividly because I had to patch some games to make them work on my machine.
What I recall is that the I/O Port A8h only worked on the Expert, while the HB-8000 required writing to a "magic" address somewhere in the address space. The mechanism on the HB-8000 actually resembles what's documented for secondary slot mapping in MSX2.
The msx.org wiki states
the Hotbit followed MSX standards strictly unlike the competing Gradiente Expert
But my recollection is just the opposite: A8h I/O was the MSX Standard way of controlling the slot mapping, and the HB-8000 implementation was non-standard.
Where can I find documentation on the HB-8000 way of doing it? And which one was standard?