28 Jun
2023
28 Jun
'23
1:48 p.m.
On Wed, Jun 28, 2023 at 6:00 AM Grant Taylor via cctalk
<cctalk(a)classiccmp.org> wrote:
Tony's email makes me ask more questions than I have (smart alack)
answers to. Maybe ~> hopefully I can ~> will learn something.
I was being a bit of a smart alec too. The point I was making is that
a bit of normal IDC ribbon cable is not electrically the correct cable
for an AUI interface but it won't matter over a few inches.
The correct cable is 4 twisted pairs with a overall screen (shield).
One pair is thicker wires than the other 3 and is used for the power.
This cable was very hard to get by the metre when I needed some about
30 years ago, and a full reel was several hundred pounds. I was lucky
enough to be given a couple of metres as an 'offcut' by a gentleman
who worked in network support. You probably need something like that
if you're makng a 1m cable. But not for what the OP is trying to do.
On 6/27/23 10:26 PM, Tony Duell wrote:
There are 2 problems with the wrong cable. Firstly will it carry the
current for the power supply pins? My experience is that it will, at
least for most transceivers.
The second is that the characteristic impedance is wrong. It's
actually not too far off but... This will cause reflections. It won't
matter on a few inches as the reflections will take about a nanosecond
to get back and will die out in << the bit time. It may matter on
longer cables.
For a few inches, which would be enough here I
think, I've used an IDC
DA15 plug and socket crimped onto the normal ribbon cable. Technically
it's wrong but the reflections on that length of cable won't matter.
Isn't 10Base<something> quite resilient? Especially at these distances?
Though I don't know if AUI is considered 10Base<anything> in and of
itself. Doesn't it become 10Base5 / 10Base2 / 10Base-T based on what
transceiver is on the other side of / attached to the other end of the
AUI cable?
AFAK AUI is not 10baseAnything for the reason you give
I'm assuming that MAU is meant for multiple stations to connect an AUI
MAU is something like 'media access unit' and is the official name for
a transceiver. Due to the fact that there had to be a certain distance
between transceivers on the cable, there were things that had multiple
AUI connectors to link to computers (these were normally male DA15s on
the unit, so a normal transceiver cable would work) and a further AUI
connector (normally a female DA15) for a transceiver onto the 'real'
ethernet. DEC's DELNI is a common-ish example of such a unit, I think
the printset is on bitsavers
cable into and it then connects to the ostensibly
10Base<something>
network. -- I originally read and was replying as if Chris was trying
to take the AUI port on his Pro/380 and connect it to an AUI port on a
hub / switch. My concern being that both AUI ports would be the same
gender and assuming that there are (at least) a pair of transceivers
converting each device from AUI to 10Base<something> to connect to each
other.
There is no real equivalent of an 'AUI null modem cable' (should that
be 'null transceiver cable'?)
If you want to link 2 computer-type ports together you need the
equiavelent of 2 transceivers. Probably the easiest is a pair of
10baseT transceivers and a crossover 8p8c cable
If you want to link 2 transceivers together on the AUI side then
that's a network bridge. Even a basc one is quite a lot of
electronics. If you want it to only pass on packets for particular
machines then it gets very complicated, one that I picked up last year
contains a 68020 CPU _and_ a board containing a 16 bit processor made
from 2900-series bitslice stuff
-tony