Re: [SI-LIST] : How to identify SSO

D. C. Sessions (dc.sessions@tempe.vlsi.com)
Thu, 08 Jan 1998 08:05:54 -0700

Andrew Ingraham wrote:
>
> > One thing that has always concerned me with SSO is the affect of the VCC
> > drop on non-switching signals. Theses signal would have noise on them
> > that would mimic the VCC noise on chip (since their outputs are
> > effectively shorted to VCC).
>
> Indeed. Even worse, since noise margin is usually smaller in the
> low state than the high state, is the GND bounce killing your noise
> margin on those outputs that are supposed to be LOW.
>
> You may need to assume that ALL outputs go indeterminate on every
> clock cycle, whether they switch or not. Clock or clock-like
> outputs need special treatment to keep them usable as clocks.

Absolutely. Synchronous systems specifically tolerate noise on
non-switching signals except during sample windows, which moots
the noise issue. Clocks, IMNSHO, should be differential signals
anyway for a whole slew of reasons, this not least.

-- 
D. C. Sessions
dc.sessions@tempe.vlsi.com