On Wed, 5 Jan 2000, Scott Presnell wrote:

> Hi Folks,
> 	Sorry to post such a simple question.
> 
> 	I've used NetBSD on i386 for some time, but I've found myself considering
> using a product that speaks RS442/RS485. I could use a spare Centris 650 to communicate
> with this device, but couldn't find a direct answer to this in the FAQ or mailing list
> archive.  I couldn't find strings such as RS232 or RS422  or localtalk (which runs over
> RS422 correct?) in the source code.
> 
> 	So: Does port-mac68k support RS422 protocol communications on the printer/modem port?

RS422 isn't a protocol. It's a signaling standard. As a crude
approximation, it's RS232 but with differential transmit and receive. i.e.
a "1" is v+ > v-. RS232 is a "1" is a voltage between -3V and -12V (or was
that -25?) relative to "ground". Yes, a "1" is a negative voltage. :-)

That's why you can go from one to the other with just a cable.

It's been a while since I played with RS442/485, but I think the signaling
is different for them. I'm not sure if just a cable will work. RS485 is
the differential version of RS442.

Take care,

Bill