MC68000 "size" (was Re: modern serial terminal)

woodelf bfranchuk at jetnet.ab.ca
Thu Nov 8 11:43:04 CST 2007


Lee Davison wrote:
>> There's a reason I described the 68000 as a 16/32 processor earlier
>> today... internally it *is* 32 bits.  The bus interface is just reduced
>> to save on the pin count, etc.
> 
>> Look at the size of the ALU and the accumulator(s)/data registers, then
>> come back to me.
> 
> The MC68000 only has a 16 bit ALU and longword operations are done in
> low/high word sequence. This is why some longword operations take two
> more cycles than their equivalent word forms.
> 
> Lee.
All this red herring's is about the data path.
The address calculations are done 32 bits rather than
intel's segment offset 16 bit hack. The real cry is you don't
have 32 bit direct addressing[2] on the 68000 so it is not 32bits.
What could use it today as modern[1] OS's don't have static addressing anymore?
Ben.
[1]Something after the 70's not running Fortran.
[2]pointer indirect is normal array accessing, not static.




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