Re: Appletalk/Phonenet box wiring (Re: ...phoneNet connection to Win2K?)

[mister_boffo@hotmail.com (Mister Boffo)]

On Wed, 11 Jul 2001 15:41:26 GMT, russotto@wanda.pond.com (Matthew
Russotto) wrote:

>In article <3b4c6986.212088632@news.mw.centurytel.net>,
>Mister Boffo <mister_boffo@hotmail.com> wrote:
>>
>>It is possible that R3 and R4 don't "protect" RxD+/- but instead are
>>there to make sure some power flows through the transformer from TxD+
>>to TxD-. Without R3 and R4, all the output of TxD+/- could be sucked
>>up by RxD+/- without doing anything in T1. 
>
>I think it might be a bit more subtle than that.  The probable reason you
>need a connection from your own transmitter to your own receiver is
>for collision detection.  With a straight connection, your own signal
>would overwhelm any signal from the bus, leaving you unable to detect
>collisions. 

You may have missed the earlier part of this discussion. The receiver
and transmitter are connected to each other since that's the only way
for the bidirectional Appletalk bus to connect to both of them at
once.

However, yes, I do think I see what you mean. You can check for errors
by sending out data, and then immediately checking if you can read it
back on the incoming side okay. If the data comes back garbled then
there was probably a collision.

Overall it's a rather weird way to use your serial port. :)

Honestly, I don't think there is anything at all different between the
serial and modem ports on a Macintosh if this is all there is to it.
Appletalk appears to involve no additional hardware beyond the normal
serial port, and AppleTalk may be a completely software-based network.

Apple always claimed the printer port was for AppleTalk, but I don't
see any objective reason why it matters which port get used. Perhaps
Apple used more expensive serial hardware for the printer port, so
that it could signal much faster than the modem port? Anybody know
what the max speed is of the modem port vs printer port?

-Mr. Boffo