semi-homemade micro

Allison ajp166 at
Sun Nov 13 20:10:27 CST 2005

>Subject: Re: semi-homemade micro
>   From: woodelf <bfranchuk at>
>   Date: Sun, 13 Nov 2005 17:19:15 -0700
>     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at>
>Allison wrote:
>>What do you mean by "Well what about them?"?
>Tell me more about them!  Non 8 bit word length computers.

I think there is a 22bit forth machine out there and ofcourse people 
have done FPGA PDP10 and I also heard once someone doing an 18bit

>All my small C stuff  is stored safe in my bitbucket.   It has too many 
>8080 design gotya's to generate code for the cpu design  I have now.
>I don't have register to regsister addressing and indexing from the 
>A register.

And that stopped you?  really I have a SmallC compiler that produced
ok 8080 code.  By OK it's as good as an 8080 can do.

>Out here all the junk is dead PC's. :(

Thats largely what we have here these days.  However 386 and 486 
board have nice cache rams some TTL and the like.  That and I find
in piles.

>>Want to try an emulation project?  take a 8048 or 49, strap EA 
>>(uses external rom then) and write a program to make port 0 and 
>>some latches and stuff on the bus port look like a version of
>>your favorite CPU of any word length.  Sure it will be slow 
>>(8049 @11mhz run instructions at 1.3us) but different! hang 
>>ram rom and IO even front pannel on the emulation and you have
>>anything you can imagine and fit in 4k or eprom and 128bytes 
>>of internal ram (8049). Those 8048s and 49s are common and 
>>easily found in keyboards (LK201 has the faster better 8051!)
>>and is a cool old cpu to work with.
>That is a nice idea!

Everyone has done the PC emulating whatever.  Why not take a single 
chip micro and use that to emulate another micro as hardware?  Same 
idea maybe slow but for a lot of things speed is not the whole world.
I did it on paper for PDP8 and it was possible using an 11mhz 8049 to 
come within 1/10 the speed of a real 8.  I guess a 36bit machine could 
be done as well (though really slow.).  Also a front pannel could be 
programmed into it as well (maybe a speed hit).  Any cpu that gets 
an instruction from memory and then executes it can be emulated that 


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