News from Mac OSX - Mysterious Serial Port

[Dar Scott]

On Friday, August 22, 2003, at 07:25 AM, Stephen Quinn Barncard wrote:

> Rather than destroy a cable or mess with those horrible mini-dins, I 
> would use a mini-din to DB-9 adaptor (still available), then wire a 
> DB-9 Female (or male, i forgot).

Good idea.  I didn't realize they were still around.

Another idea is to build that adaptor with an old cable.  I currently 
make my adaptors adapt to the DB-9 and then use null modems and 
extenders and loop-backs on that, but I'm currently partially DB-25.  I 
never did get on the RJ-45 craze for RS-232.  (Notice that I never mess 
with "those horrible mini-dins"--was so even before the hands got 
rusty.  Besides, they are hard to find.)

One potential problem is the handshaking.  The mac has only one in and 
one out and I'm not sure how they work.  I'd make one with none and one 
with those connected to RTS and CTS.

I have a power supply which a Mac cannot talk to.  It needs a strong 
RTS to power the optical isolation circuit.  I love the idea of 
isolation.  The signal ground and the signals are isolated.  But they 
got cheap and powered it from the RTS.  The data that came with it 
indicates that the Mac output handshake line will not work.

In general, RS422 is not RS232 and any setup might have problems.

BTW, there is no standard (that I know of) for RS422 DB9, the adaptor 
I'm describing above is for emulating RS232 on DB9.

It is possible to get 422 to 232 adaptors which are electronic level 
converters and sometimes isolated.  This might allow one to exploit the 
distances one expects from 422.

And while I'm babbling, I think it is possible to use mac in a two-pair 
RS-485 situation in some configurations.

Dar Scott

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