Conclusion

MT16 would have been a short form for
"My transistorised 16 Bit CPU."

As the name indicates, MT15 would not qualify as a
"full/complete" 16 Bit CPU.
There isn't a dedicated JSR/RTS instruction, and it makes
no efficient use of program memory.

It would be nice to have a JSR command like with some
Forth CPUs.
Means, OpCode Bit 15 = 0 would indicate a 16 Bit word
containing the address of a subroutine to be executed.

Program memory use would be more efficient with a higher
encoded instruction set,
dividing a 16 Bit word into an 8 Bit OpCode and an 8 Bit parameter.
So we could handle pointers like with the 6502 in a "Zero_page".

For 16 Bit parameters, $80 (decimal -128) in the 8 Bit parameter field
may indicate to fetch the next 16 Bit word as the "real" parameter.
(Some of you probably remember the 68020 branch instructions...
or the addressing modes requiring the extension word...)

Addressing modes like postincrement/predecrement would also have
been a nice thing.

Of course, I am dreaming.

The situation was, that I did solder plenty of SMD components for
at least six months, without knowing if MT15 would ever work at all.
So I wanted to go with an architecture and an instruction set as simple
as possible.

But since I learned something while building it, there could be some
educational value to this project.

Some of you should have noticed already, that the use of transparent
latches for T0, T1 makes the CPU a little bit inefficient.
Unfortunately, building reliable, capacitive coupled, edge triggered
flipflops with a propagation delay < 1us with low_frequency transistors
may turn out to be difficult.

You sure could imagine, how to build a better CPU.

Now to take a break, before trying to further improve my skills
in building flipflops and logic gates.

Starting wo wonder, what to build next...

Well.
You have seen, how to build your own CPU from simple components,
that are supposed to be still in production in the year 2035.

And that things, that look simple at first sight, may take
more time to develop than those who look complicated.

Nervertheless, you shouldn't try to build such things at home.

One final warning:
Building your own CPU may increase your knowledge, how things work.
Increasing your knowledge may be hazardous to your health.
You can't buy anything for knowledge.
And it only may ruin your good nights sleep, when knowing too much.

Life is easier, when swimming with mainstream, and not against it.

So please, close this text and don't think about building own computers
any further.

...so much for the use of reversed psychology.

[HOME] [UP]/ [BACK] [1] [2] [3] [4] [5] [6] [7] [8]