9 Aug
2006
9 Aug
'06
7:13 p.m.
The MAU is not just an amplifier, there is logic there
too. Besides the
two data pairs, there's a third "control circuit" that propagates things
such as link state, collisions, etc. from the MAU to the ethernet card.
For a standard MAU -- that is 10base5 of 10base2 to AUI, there's very
little logic in there. I've got a couple built from essentially discrete
components with a couple of 10K ECL chips (the signal pairs are
essentailly transformer-coupled ECL signals, of course). IIRC those chips
are just line drivers and receivers.
The 3rd pair (at least in the origianl implementaion) is for collision
detect. As I mentioned the other day, the transmitter is a current source
that develops a voltage across the termination resistors of the coax
cable. If 2 devices transmit at once, you get twice the voltage across
the resistor (==between inner and outer of the cable). This is detected
and used to provide the collision signal.
-tony