64-bit CPU

[John Macdonald]

On Fri, Sep 17, 2004 at 08:14:38PM -0400, James Knott wrote:
> John Macdonald wrote:
> 
> >I've got the "TMS Microprocessor Data Manual" on my bookshelf,
> >it is dated November 1975.
> >
> 
> I think I had (have?) one of those too.  Back in the 70's, I had several 
> books on different CPUs. I seem to recall one, that used serial I/O for 
> everything, including memory.

Using serial I/O to access memory is not the 9900.  It had
a 16-bit data bus and a 15-bit address bus (it only used
16-bit word reads and writes - I think it had to do a read/
modify/write sequence to write a byte into memory).

Serial I/O only interface sounds more like the microprocessors
that were aimed at device controller purposes; which had a
small amount of on-chip memory that was directly accessible
and only I/O interfaces to off-chip resources.  There were lots
of them that were variants of the 8-bit processors.  The point
there was to not require a memory interface and memory chips,
with the corresponding interface control lines and logic chips.
That kept the chip count and cost down for a device controller.

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