Homebuilt TTL and transistor CPUs - wierd logic

[Chuck Guzis]

On 1/24/2006 at 8:00 PM Jim Battle wrote:

>No, my memory was that it used 4-state cells to encode two bits per cell 
>in the microcode rom.  Rather than transistor/no transistor to represent 
>0/1, it used no transitor = 00, weak transistor=01, normal 
>transistor=10, strong transistor=11, or something akin to that.

Quite correct!  I found a couple of citations in the IEEE online archives.
My muddled mind had it as (zero, one and neither).  I understand that some
flash memories also use 4-valued (quaternary) memory cells "under the
hood".  

I wonder if eventually multi-valued logic may have its biggest potential
not in speed or conservation of chip space, but rather in decreasing the
number of I/O pins.

Cheers,
Chuck