On Thu, May 27, 2004 at 12:27:27PM +0100, Bert Thomas wrote:
> I don't understand why you need a converter anyway. RS422 and RS485 use
> the same voltage levels AFAIK.
There is overlap between the permissible levels for RS422 and RS485, but,
officially, if you graph out the voltages and permissible sink currents,
they are not _required_ to be in the same range.
> There is basically one situation that has to be avoided and that is two
> transmitters connected at the same time. If you say that you RS485
> device has 4 wires, I'd guess it has 2 for sending and 2 for receiving,
> so it would simply connect easy to the RS422 device.
In my particular case, the one device happens to be a 4-wire send/receive
double pair... I was just concerned about being formal and proper and
hooking two devices together via buffered interfaces.
> BTW, a common mistake is that people think that since RS422/RS485 are
> differential busses, the ground does not have to be connected. I once
> red a very good article on this topic that explains that the grounds of
> all devices should _always_ be connected.
>
> Correct me if I'm wrong.
AFAIK, your ground reference needs to be common in nearly all cases.
> --
> One thing I just wondered: in what time zone do you people at the
> southpole live?
We happen to keep NZ time, specifically because planes come from
McMurdo Station which also keeps NZ time, because their planes
come from NZ. That way, nobody has to worry about time shifts.
Here at Pole, obviously, we could keep any time we wished. The
typical desire is to synchronize with our flight schedule.
Otherwise, we might as well keep GMT to make the scientific data
collection easy (all of our logs for the experiment are kept in
GMT).
-ethan
--
Ethan Dicks, A-130-S Current South Pole Weather at 27-May-2004 13:20 Z
South Pole Station
PSC 468 Box 400 Temp -86.4 F (-65.8 C) Windchill -122.8 F (-86 C)
APO AP 96598 Wind 8.5 kts Grid 070 Barometer 681.4 mb (10571. ft)
Ethan.Dicks_at_amanda.spole.gov http://penguincentral.com/penguincentral.html
Received on Thu May 27 2004 - 08:30:33 BST