1 May
2012
1 May
'12
2:43 p.m.
it strikes me that one of the main moans about RS232
was that there
were straight cables and null-modem cables and this confused people.
If it had been agereed that all 'hosts' -- that is computers -- would
be wired as DTEs, and all 'slaves' -- modems, printers, etc -- would
be wired as DCEs, there would bne no problem.
Well, that was pretty much the idea, as I understand it.
But, as you say,
The problem arrose because you could link
'hosts' (computers)
directly togther with RS232.
And that's what a null modem is for. Conceptually, it's two
back-to-back modems, implemented by non-straight-through wiring in the
cable (or connector or whatever).
Twisted-pair Ethernet appears to have learned nothing from the
serial-line confusion; it went with two different wirings (`host' and
`hub') and thus repeated the straight-vs-crossover cable issue in a new
field. It would have made so much more sense, even more than for
RS-232, for everything to have the same wiring, so there's only one
kind of cable involved. Instead, we had two kinds of cables for a long
time, and even now we have special hardware capabilities (called
"auto-X" or "auto-MDI") to compensate for the whole mess.
RS-232 can, to a degree, be excused by its vintage; when it was
developed, the zeitgeist was much more heavily into the DTE/DCE
dichotomy than now. Twisted-pair Ethernet had much less excuse.
USB seems to avoid this my simply making it impossible
to direclty
link 2 hosts. I ds not see that as an improvement!.
Agreed! Totally agreed.
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