Have you looked carefully at the instruction set? A careful inspection of this will reveal some patterns. For example:

the ADD instruction:

high nibble is 0010
low nibble describes the address mode. If low nibble is 0100 next byte is immediate data.

the ANL instruction:

high nibble is 0101
low nibble describes the address mode. If low nibble is 0100 next byte is immediate data.

the ORL instruction:
high nibble is 0100
low nibble describes the address mode. If low nibble is 0100 next byte is immediate data.


we can see a pattern emerging here.


Then for the control unit of the processor you have a choice of two implementations: microprogrammed or random logic. I would say the original 8051's were microprogrammed since you have 12 clocks to a major cycle whereas the newer 1 clock 8051's I would suggest are random logic.

As Andy suggessts, you need to find a good book on processor design or do a lot of searching on the web. This is a large topic!


Here's a start:

http://en.wikipedia.org/wiki/Microcode

I'd suggest looking at a PIC for starters - the instruction set is much simpler as is the whole cpu.

There's a book, probably long out of print by Mick and Brick that goes through the whole method of designing a microprogrammed processor.