Re: [NTLK] NEEDED: cables

On 05.02.2009, at 16:55, James Fraser wrote:

> Hello,
>
> --- On Thu, 2/5/09, James Fraser <wheresthatistanbul-newtontalk@yahoo.com
> > wrote:
>
>> The PS/2 device in your link has 6 pins; the port in the
>> Keyspan serial adapter has 9.
>
> Correction:, that should read "the port in the Keyspan serial
> adapter has room for /8/ pins." Sorry about that...

Um, ok, so there are a bunch of ports and plugs that are confusing.
I'll try to explain:

All Newton related serial connections use the "classic" terminal
protocol. In contrast, the USB is also a serial connection, but uses a
bus type of connection. It is not compatible to the classic serial
protocol. This is where you need the USB-to-serial adapter.

Next, the elektrical characteristics:

PCs use RS232 at voltage levels of 15V to represent a logical 0, and
-15V to represent a 1. These usually come as the Sub-D 9 or 25 pin
connectors. They have relatively large pins and the classic "D" shape.

The Apple serial port and Apple Talk use RS422 which is based on a
differential power loop signal and is incompatible to RS232!

The Newton serial port exists in two versions: the blocky Interconnect
port is compatible to RS232 and RS244 and requires a relatively
expensive and propriatar adapter. The adapter has a whip with either a
9 pin Sub D plug that goes into the PC, or a 8/9 pin Mini DIN plug
which goes into the APple serial port.

The 8/9 pin connector on earlier Newtons and the EMate is a RS422
connector that goes right to the Mac. It is possible to connect to a
RS232 port, but again requieres a special adapter, create by Apple for
this purpose (Apple was smart enough to have the Newton RS422 ports
switch into RS232 mode if it discovers those voltages).

There is yet another kind of serial connection that uses Mini DIN
plugs, but not the 8/9 pin ones, but the 4 pin version. These are PS/2
ports and use different voltages (0 and 5V) and a different protocol
(asynchronous) and are not available to a PC as a serial port. They
are specifically made to connect keyboards and mice to a PC. They are
of absolutely no use to Newtons.

Finally, I kept using "8/9 pin" as a connector size. This is not
because I can't make my mind up about the pin numbers, but for a very
Apple specific reason: when Apple introduced their serial port, they
needed 8 pins for all signals. So they decided to use 8 pin Mini DIN
connectors. Later, Apple figured it would be nice to provide an
additional 5V on the serial plug, however the 9 pin Mini DIN is not
compatible to the 8 pin Mini DIN. Apple's solution: they squeezed an
additional pin into the 8 pin plug, staying compatible to old systems
(and making it impossible to buy any of these plugs).

(DIN = Deutsche Industrie Norm - German Industrial Standard)

Matthias

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