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

[russotto@wanda.pond.com (Matthew Russotto)]

In article <3b507efb.217582471@news.mw.centurytel.net>,
Mister Boffo <mister_boffo@hotmail.com> wrote:
>On Wed, 11 Jul 2001 15:41:26 GMT, russotto@wanda.pond.com (Matthew
>Russotto) wrote:
>
>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.

Appletalk requires RS-422 drivers and a serial controller capable of SDLC
communication at 230Kbps (I think using NRZi encoding, but it's been
way too long since I traced this).  A simple asynchronous RS-232 port won't
work.  But you're right -- there is no hardware difference between the
serial and modem ports on the Macintosh.

>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?

For the Lisa, only one of the ports was RS-422, so you had to use that one.
For the Mac, the difference had to do with the floppy disk driver.  It
disabled interrupts, which could cause lost characters.  This didn't
matter much for AppleTalk, which is expecting that sort of thing.  But
it causes problems with modems.  So the floppy driver polls the modem
port periodically while interrupts are disabled.  The printer port is
left to its own devices.

-- 
Matthew T. Russotto                                russotto@pond.com
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue."