Re: //gs LocalTalk Port

[dempson@actrix.gen.nz (David Empson)]

Nathan Mates <nathan@visi.com> wrote:

> In article <359B4A56.3CF6B79D@netcomi.com>, Dan Bethe  <dtm@netcomi.com>
> wrote: 
> 
> >Oh, so if I did Appletalk between a //gs and a Linux pc, it would work
> >at a maximum of 57600bps?  But if I did Appletalk with a //gs and a //gs
> >or Mac, then it would be at a happy 230kbps?
> 
>    No. Appletalk is ONLY at the 230kbps speed, asynchronous.

No, LocalTalk is 230400 bps SYNCHRONOUS.

> Modems (and all other normal serial transmissions, such as printers, null
> modems and the like) are up to 57.6kbps, synchronous.

No, they are ASYNCHRONOUS.

Synchronous means clocked: LocalTalk uses Manchester coding, in which
there are one or two transitions per bit cell, with the clock being
recovered and kept in phase with each bit.  Some synchronous
communication methods use a separate clock signal.  There is no
per-character data overhead, though there is usually frame-level
overhead and possibly inserted bits or bytes to handle data
transparency.

Asynchronous data is not clocked.  The sending and receiving devices
need to be set to communicate at the same data rate (or auto-detect it
from receive data, in the case of modems).  Characters have start and
stop bits, and the start bit is used to determine where character
boundaries are located.

>    The Appletalk card or an external device to go from Ethernet <->
> Appletalk

LocalTalk (the physical layer and data link protocol), not AppleTalk
(the entire protocol stack).

>    Well, ip-over-appletalk is specced out as a protocol, but Apple
> couldn't be bothered to support such a thing.

See my other post.  It has been a standard feature in MacOS since Open
Transport was released, and has been supported for a long time before
that with add-on software.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand