Re: Getting a IIgs to play nice with a Mac

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

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?
> > >
> > > good chance...
> > 
> > Very good chance. A pair of Mini-Din-8 to DE-9 or DB-25 adapters would
> > only work together if you used a crossover serial cable between them.
> 
> I was trying with a mini-din to D9 M on one and mini-din to D9 F on the
> other.
> I can confirm the Male D9 one is fine straight off. I've used it for ADT,
> ZModem etc.
> ..As for the one with the D9 F, err... I'm not sure where it came from.

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).

> > AppleTalk with a "null modem" cable only requires the data lines and
> > ground.
> > 
> > If you use a Mini-Din-8 to Serial adapter you are also clobbering half
> > the balanced serial signal (the RX+ input is grounded and the TX+ output
> > is not connected) but it will probably work as long as you end up with
> > the ground lines connected and Tx/Rx crossed over.
> 
> There is a chance it could work because of the way the signals are converted
> but I'm less than sure.

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).

It would be best to wire both RX+ and RX- through to TX+ and TX-, using
a Mini-Din-8 at both ends and no adapters.

That means connecting the middle pin (4, ground) straight through,
swapping over the outer pins of the middle row (3 & 5, TX- and RX-) and
swapping over the outer pins of the third row (6 & 8, TX+ and RX+).
Don't connect the other three pins, or if you must then swap 1 & 2, but
let pin 7 go straight through (which will give you a full 8-way
crossover cable).

> Anyway, I found where to get the right mini-dins for AU$1.50 each so I'm
> going to order them in a couple of weeks time.
> 
> There is one thing that I'm curious about. If I can get data across via the
> double serial adaptor, there would be at least a slight chance I could get
> appletalk working, right? I haven't tried that yet.

I would steer clear of that D9F adapter unless you've been able to
document its pinout.

The D9M adapter should be easy enough:

Mini-Din-8      D9M
1 HShkOut       7 RTS or 4 DTR, depending on desired function
2 HShkIn        8 CTS or 6 DSR, depending on desired function
3 TxD-          3 TxD
4 GND           5 GND
5 RxD-          2 RxD
6 TxD+          n.c.
7 GPI/DCD       1 DCD (probably)
8 RxD+          5 GND (to correctly bias the receiver)

I haven't memorised the original Mac D9F pinout so can't suggest the
likely pinout of that one.

> I'm hoping that I can find the other mac to PC adaptor that came with a Palm
> cradle that I think I have. It would make things a little easier.

-- 
David Empson
dempson@actrix.gen.nz