22 March 2010, John Dore tells me that USB has
been using bidirectional signalling down one twisted pair for some years.
This means that the section below, which I added to http://www.ivorcatt.co.uk/x0357.htm
yesterday, means that I was waiting for something to happen which had
already happened. But see
should mention that over the decades I have spent enormous time on Heaviside, and my interpretation of his “duplex
telegraphy” was not to send signals in two directions down the same
wire(s), as John Hunt seems to say. I thought that the idea originated with
me in the context of today’s computers for the interconnections between
computer and printer, for instance. Until today I kept it secret. I do hope
my co-author Mike Gibson, who is the top expert in the world on Heaviside’s writings, will clarify this.
is quite extraordinary that today ‘Duplex Telegraphy’ has been forgotten.
There is a crying need for two way signalling
using the same conductors between modules, for instance computer and
printer, in today’s computers. I have watched with amazement the failure of
the industry or the profession to move to two way signalling. For me, the
ideal is to have only two conductors between a pair of modules, signal and
ground, and work the line with high speed serial. This gives major cost
advantages, and makes failure modes easier to detect because catastrophic.
However, at least, after a delay of a decade or two, the industry has moved
from ghastly fully parallel to serial intercommunication. John Foggitt will confirm that I was arguing for serial more
than a decade before the industry moved from parallel to serial. I have
kept quiet about what Heaviside called “duplex”
signalling, and waited to see if the industry would realise that that is
the proper way for inter-module intercommunication. This is the first time,
22 March 2010, that I have mentioned it anywhere.
It is easy to do. The key is to use the ECL circuit.