I think RS422 is a 'bus' type architecture - i.e. you can have multiple
units tied to the same port - the protocal is 'packet' oriented, and each
packet has an address - so you may have a protocal problem as well as an
electrical interface problem. Not sure - memory getting bad.
Dave K5WNV
----- Original Message -----
From: "Duane Grotophorst" <n9dg@yahoo.com>
To: <tentec@contesting.com>
Sent: Saturday, June 07, 2003 6:58 PM
Subject: Re: [TenTec] hp Z3801A GPS Unit
>
> Here's a web site that can give you much of the
> pertinent information for RS232 vs. RS422 plus some
> other somewhat common serial specs.
>
> Disclaimer: I know nothing of this particular company
> good, bad or otherwise, but found the above referenced
> web page to be very informative.
>
> http://www.rs485.com/rs485spec.html
>
> Much of the broadcast equipment that is driven by the
> software that I work with is RS422 instead of RS232.
> In most cases we specify PCI plug in RS422 serial
> cards for the control computers running our software.
> In some cases we can use an RS232 to RS422 converter
> with good reliability. I doubt if you will be
> particularly successful at simply connecting RS232
> with RS422 without a proper level converter. Should be
> able to find one of those beasts for around $60-100.
> Just do a search for "RS232 RS422 level converter"
> should get many hits.
>
> Another thing to consider/watch out for is that
> pin-out standards for RS422 are lacking to say the
> least, the Sony VTR control standard is quite common
> in the land of broadcast equipment, - but don't count
> on it being universal. Bottom line is you need the
> documentation for each piece of gear you have and make
> the required cable accordingly.
>
> The fundamental difference as already described below
> is that RS422 is a differential signaling scheme with
> +/- TX/RX pairs going both directions (4 wires) and
> RS232 is ground referenced.
>
> Duane
> N9DG
>
>
>
> --- Jim Reid <jimr.reid@verizon.net> wrote:
> > With regard to the 232 and 422 data formats, I
> > wondered:
> >
> > > >Can I just now connect them together, or are
> > they different
> > > >voltage levels; thus the need for the
> > "interface" unit
> > > >previously discussed??
> >
> > Eric responded, in part:
> >
> > > I think the interface levels are different, and
> > the proper
> > > way of dealing with RS422 is with separate grounds
> > for each
> > > datapath.
> > >
> > > I don't know if it is necessary, however.
> > >
> > > RS232 is very forgiving, so I doubt you'd do any
> > harm in connecting
> > > them, but... you may have to switch 2 and 3 to get
> > a null-modem
> > > connection. As for the (B) lines mentioned in the
> > diagram, I don't
> > > know if they're necessary for RS422 or not.
> >
> > Believe, with some searching about have uncovered
> > what the
> > 422 system is about:
> >
> > "A pair of wires is used to carry each signal. The
> > data is encoded
> > and decoded as a differential voltage between the
> > two lines.
> > A typical truth table for a balanced interface is as
> > follows:
> > VA-VB < -0.2v =0
> >
> > VA-VB > +0.2v=1
> >
> > As a differential voltage, in principle the
> > interface is unaffected
> >
> > by differences in ground voltage between sender and
> > receiver."
> >
> > So, with the set up I now have, I have omitted the
> > B path
> >
> > of the differential pair! However, it seems to me,
> > that if there
> >
> > is 0 voltage on A, that the bit is still 0; and if
> > A is high, then
> >
> > the bit is 1, correct?? If not, I will have to go
> > back in and
> >
> > add the wires for the pins 14 and 16 from the hp
> > unit's
> >
> > female DB25 in order to pick up the differential
> > pair performance.
> >
> > I may still not understand all of this, hi.
> >
> > 73, Jim KH7M
>
>
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