Re: Appletalk on IIC

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

Nathan Mates <nathan@visi.com> wrote:

> In article <3365065f.0@news1.ibm.net>,  <wshek@ibm.net> wrote:
> >>However you do need additional hardware - probably a box with a 65c02 and
> >>a z8530 that would connect to the serial port of the //c and have an
> >>Appletalk port - and no one has one of these to my knowledge.
> 
> >I'm not understanding why you need extra hardware, the mac doesn't use it?
> 
>    No, the Mac and GS have that built in. The serial controller chip
> on the //c is incapable of dealing with Appletalk, and needs
> (nonexistant) addon hardware to do the job.
> 
>    Same reason why a //e with Super Serial Card (or clone) or PC can't
> do Appletalk right out of the box-- Apple used nonstandard serial
> chips to pull off Appletalk in the first place.

I take issue with that statement.  The so-called "nonstandard" Z8530
chip used was released by Zilog in 1981, and is still being made and
sold in large quantities (even if you exclude Apple's use of derivative
versions).  It supports more serial interface protocols than almost any
other serial chip (except high-end ones like the Zilog USC, or some
Cirrus Logic chips).  In recent years there have been improved versions,
such as the Z85230 Enhanced SCC, which we use at work in some embedded
applications.

When the Mac was released, the Z8530 was the only serious choice for a
flexible serial chip that supported sync as well as async communication.

LocalTalk was an excellent design at the time it was invented.  It is
only in recent years that Ethernet has become cheap enough to seriously
threaten LocalTalk as a low-cost network.

The Z8530 allows all sorts of useful applications.  Look at the
QuickTake camera for example - it uses one of the high speed clocked
synchronous modes available in the Z8530, with data rates over 1 megabit
per second.  Using one of these devices on a PC means using a relatively
low-speed asynchronous serial connection (115200 bps).

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