Some findings on Mitsubishi 7700 core and microcontrollers - it's a bit like an 816 but without the 6502 compatibility mode. Up to 25MHz. It retains m and x mode bits, has a prefix byte to bring a B accumulator into play, and includes multiplication and divide using another prefix byte. Both A and B are 16 bits and usable also byte sized.
(
500 page user manual (MITSUBISHI 16-BIT SINGLE-CHIP MICROCOMPUTER 7700 FAMILY / 7700 SERIES 7702/7703 Group User's Manual) - gone from there, now found
here. Or try
here instead for a 344 page version)
http://www.alcyone.org.uk/ssm/7700sm.pdf (361 page software manual) (programmer's model page 11)
Then the 7900 (source code compatible) introduces 32 bit operations, 100 extra instructions, and 20-30% code size reduction. Has 4 direct page registers and a 32 bit accumulator E (concatenation of B and A.) Also RMPA, a vector product instruction.
https://www.renesas.com/sg/en/doc/produ ... 7900sm.pdfEdit: see also previous threads
Edit: thanks to anonymous donor, added a link to the 512-page User's Manual.