Iggy Drougge wrote:
>
> Tony Duell skrev:
>
> >> I don't think I could form any relationship to a 4-bitter, either. I woul=
>
> >Oh, there are a lot of them about. Of course it depends what you mean by
> >'4 bit', but if that's the ALU/bus width, then the HP Saturn processor (used
> >in the 71B, 28, 48, 49, etc, etc, etc) is a 4 bit chip. And I certainly like
> >those machines (and yes, IMHO they are computers rather than calculators).
>
> I have no idea what you're on about. =)
> Besides, a 4-bit address bus seems utterly, utterly limited.
It gets better :-) . It is a multiplexed data/address bus; thirteen
wires including ground and power, that's it. Four lines are
data/address. The rest control the bus state and the soft
configuration of the base addresses of all devices. The
original saturn processor in the HP71 can access 1 meganibble, though.
In a typical cycle, first, you need to write the address to all
devices; this needs 5 clock cycles, one for each nibble in the
address. However, once the address is written, up to sixteen
contiguous nibbles can be read/written without having to put an
address in the bus. This is optimized for bcd arithmetic.
--
Carlos Murillo-Sanchez email: cem14_at_cornell.edu
428 Phillips Hall, Electrical Engineering Department
Cornell University, Ithaca, NY 14853
Received on Tue Nov 14 2000 - 11:41:00 GMT