Re: Getting a IIgs to play nice with a Mac

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

rTristan Mumford <xtristan.xmumford@xgmail.xcom> wrote:

> David Empson wrote:
> 
> > Tristan Mumford <xtristan.xmumford@xgmail.xcom> wrote:
> > 
> >> David Empson wrote:
> >> 
> >> > <aiiadict@gmail.com> wrote:
> >> > > Tristan Mumford <xtristan.xmumf...@xgmail.xcom> wrote:
> >> > >> I'm using a couple of apple serial to serial adaptors. I'm doing it
> >> > >> because I don't have an apple to apple cable. Would this be the
> >> > >> problem?
> 
> -snip-
> 
> > It could be an adapter to convert from Mini-Din-8 to the original Mac
> > serial port, which was a D9F. Its pinout has nothing in common with the
> > PC standard serial port (D9M), and connecting the two of them directly
> > together (or with a "standard" crossover cable) will at best achieve
> > nothing and at worst could damage the serial ports (unlikely).
> 
> Ah. That I didn't know. So the original mac used a proprietary D9? 

Yes. It includes all the same signals as the Mini-Din-8, i.e. it
includes both positive and negative versions of the data signals (for
balanced RS-422 operation). It is missing the General Purpose Input (pin
7 on the Mini-Din-8, used for DCD on the IIgs), but I'm not sure what
the remaining two pins do. There might be a low voltage power output.

> > LocalTalk may be fussier than standard serial, because it is running at
> > a much higher speed than typical asynchronous data, and is using FM
> > clocking within the data stream, effectively 460800 baud (230400 bps,
> > but with one or two state transitions per bit - interleaved clock and
> > data).
> 
> Now that I didn't know. I've been looking for exact info on the details of
> how the data is sent etc. Looking in the wrong places though it seems.

I don't remember offhand whether it is using FM0 or FM1 encoding, but if
you find documentation on the Zilog Z8530 SCC (Serial Communication
Controller), AppleTalk uses its SDLC mode with FM clocking.

> I also had a not so brilliant half-idea.
> I've been looking for a way to get some kind of data connection from one end
> of the house to the other. It really is a very long distance the cable has
> to traverse. It occurred to me that because of the type of signal the Apple
> cable would be more suitable.

The standard serial port on the IIgs serial port is RS-422, which is
designed to allow transmission over distances in the order of hundreds
of metres, compared to about fifteen metres for RS-232.

There are some limits due to needing to maintain a common ground signal.
Actual LocalTalk or PhoneNet cabling works better over reasonable
distances because it is isolated from each computer, eliminating the
need for a common ground. The catch is that it is half duplex, and can
only be used with a balanced data signal like FM modulation, though NRZI
might work with SDLC data. Actually using this for something other than
LocalTalk would be tricky.


-- 
David Empson
dempson@actrix.gen.nz