Spacewar! (was Re: Laser display...)

From: Tom Jennings <tomj_at_wps.com>
Date: Sun Feb 20 18:08:38 2005

> Presumably relays are prone to contact bounce as much as switches
> though, thereby introducing an analogue component into things :)

Eric's right, but I'll go further -- there is no such thing as
digital, it's all analog. It's not even semantics.

Digital logic like TTL (74xx) or CMOS (4xxx) is recognized to
behave a certain way only under certain conditions. Chips use
ordinary physics and in no way is there some macro-quantum 1 or 0
state.

Relays are not 0-ohms when closed, nor infinite when open, and
don't open or close instantaneously. The impedance across a pair
of arcing contacts is extremely and widely erratic, and arcing
occurs nearly always even if it's microscopic.

"Digital" is quite literally a state of human perception, a mental
shortcut for making things happen discretely, rather than
continuously, and hand-wave away all the mind-boggling detail.

THere's certainly plenty of times when assuming things are purely
discrete is 100% reasonable, eg. inside a CPU, but all around the
edges (IO...) you at least occasionally have non-discrete
behavior.
Received on Sun Feb 20 2005 - 18:08:38 GMT