I suspect a device I have is flipping bits before it sends out RS422
signals.  I sent 3 capital A's out of it, and the oscilloscope trace is
at:

http://www.coolgroups.com/AAA.JPG

I am using 1 start bit, 8 data bits, even parity, and 2 stop bits.  So,
does anyone know if the bits are flipped?

<b...@coolgroups.com> wrote in message
news:1...@b28g2000cwb.googlegroups.com...
> I suspect a device I have is flipping bits before it sends out RS422
> signals.  I sent 3 capital A's out of it, and the oscilloscope trace is
> at:
>
> http://www.coolgroups.com/AAA.JPG
>
> I am using 1 start bit, 8 data bits, even parity, and 2 stop bits.  So,
> does anyone know if the bits are flipped?
>

A mark is supposed to be the lowest level while a space is the highest...
the trace looks correct to me.

If you need to invert the data, a single transistor and a couple of
resistors
can do the job.

The letter A is 1000 0010 (least significant bit first).

So, are you saying it's inverted?

Lord Garth wrote:
> <b...@coolgroups.com> wrote in message
> news:1...@b28g2000cwb.googlegroups.com...
> > I suspect a device I have is flipping bits before it sends out RS422
> > signals.  I sent 3 capital A's out of it, and the oscilloscope trace is
> > at:
> >
> > http://www.coolgroups.com/AAA.JPG
> >
> > I am using 1 start bit, 8 data bits, even parity, and 2 stop bits.  So,
> > does anyone know if the bits are flipped?
> >
>
> A mark is supposed to be the lowest level while a space is the highest...
> the trace looks correct to me.
>
> If you need to invert the data, a single transistor and a couple of
> resistors
> can do the job.

b...@coolgroups.com wrote:
> The letter A is 1000 0010 (least significant bit first).
>
> So, are you saying it's inverted?
>
> Lord Garth wrote:
> > <b...@coolgroups.com> wrote in message
> > news:1...@b28g2000cwb.googlegroups.com...
> > > I suspect a device I have is flipping bits before it sends out RS422
> > > signals.  I sent 3 capital A's out of it, and the oscilloscope trace is
> > > at:
> > >
> > > http://www.coolgroups.com/AAA.JPG
> > >
> > > I am using 1 start bit, 8 data bits, even parity, and 2 stop bits.  So,
> > > does anyone know if the bits are flipped?
> > >
> >
> > A mark is supposed to be the lowest level while a space is the highest...
> > the trace looks correct to me.
> >
> > If you need to invert the data, a single transistor and a couple of
> > resistors
> > can do the job.

RS-422 and RS-485 are supposed to have two outputs, A and B.  A is
supposed to be non-inverting, and B is supposed to be inverting.  You
didn't label voltages, so I'd assume you're looking at A.

If you have a straight RS422-to-RS422 connect, If you put a logic 1
(5V) into the driver, and then you connect A of the driver to A of the
receiver, and B of the driver to B of the receiver, you will see a
logic 1 (5V0 at the output of the receiver.

If your situation is more complex, possibly you could grant us a few
more details.  Still waiting on a description of whether this is an
existing setup or you're cobbling something up.

Since you seems to be new to this, and you're also a Google Grouper (so
am I), you should know that it's considered good form to bottom post
(put your answer *under* the copy of the prior post). You should please
check out Google Groups Help Topic "What's good 'netiquette' when
posting to Usenet?"

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

Cheers
Chris

<b...@coolgroups.com> wrote in message
news:1...@b28g2000cwb.googlegroups.com...
> I suspect a device I have is flipping bits before it sends out RS422
> signals.  I sent 3 capital A's out of it, and the oscilloscope trace is
> at:
>
> http://www.coolgroups.com/AAA.JPG
>
> I am using 1 start bit, 8 data bits, even parity, and 2 stop bits.  So,
> does anyone know if the bits are flipped?
>

Yes. Those "A" bits have been flipped.

Looks like you are using the UART on a micro to format the send characters
and from the way the LSB's are being sent out first, you're also using  a
UART to receive them.

If so, the sending UART will be -absolutely- flipping those "A" bits. It
knows only of RS232 and  nothing of RS422, hence assumes it is sending data
to a Max232 type inversion chip. You can see this from the UART pin being at
+5V in a 'no data' condition.
john




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