The microcode is a series of pointers into assorted microsubroutines in the nanocode. The nanocode performs the actual routing and selecting of registers and functions, and directs results. Decoding of an instruction's op code generates starting addresses in the microcode for the type of operation and the addressing mode. [http://www.easy68k.com/paulrsm/doc/dpbm68k1.htm Source]
See: [https://gendev.spritesmind.net/forum/viewtopic.php?t=3023 Tech topic about a microcode-level 68000 core] [https://www.atari-forum.com/viewtopic.php?t=42568 New 68k core in mame] [https://og.kervella.org/m68k/ Motorola 68000 microcode]
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