25 Jun
2015
25 Jun
'15
11:05 a.m.
On Jun 25, 2015, at 1:49 PM, tony duell <ard at
p850ug1.demon.co.uk> wrote:
I see a slight difference in the input current spec of the receiver part of the
transceiver. 250 uA instead of 25 uA. That makes some small amount of sense given the
smaller station count.
>> ...
I still have a photo copied out of the 1980s
magazine RSTS Professional, which claimed to show how to convert
thick to thin Ethernet. The simple answer is ?with a coax connector adapter? since both
are 50 ohm coax. The
Err, yes :-). The BNC-N adapter is very useful :-). More seriously, I've seen
thickwire transceivers that
had a pair of N connectors (not a beesting tap) fitted with BNC-N adapters and ues on
thinwire. Technically
that is wrong, there is a minor difference in the transceiver spec (I forget what, but
the data sheet for at
least one of the transceiver ICs pointed it out), but in will work. article instead used a thinwire T connector, with
the terminator still on it. As Tony points out, terminators go at
ARGH! Ethernet is more touchhy than most as IIRC the transmitter is a current source, the
receiver effectively
senses the voltage across the terminator. A collision is too high a voltage. So ethernet
can't work with
incorrect termination.
That's why DEC had you put 2 terminators on a T piece on the ethernet BNC connector
of a VAXstation (or
whatever) to get it to pass diagnostics. WIth a network that short you are not going to
get detectable
reflection problems, but if you only had one terminator, every transmission would be a
collision.