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[DPRG] Call for reinforcements

Subject: [DPRG] Call for reinforcements
From: Eric Sumner kd5bjo at gmail.com
Date: Sat Feb 3 17:31:05 CST 2007

> Eric,
>
> I thought of this earlier but didn't say anything (shame on me).  last two
> responses now have me wondering.  Is it possible that one of these
> connections is shifted to RS-232 levels while the other connection is at TTL
> level?  I started wondering this when you mentioned that both TX and RX are
> on the same pin.  That tells me that the line is not at RS232 levels.  If
> the other board really does have an RS-232 level shifter on it (likely) you
> are probably just driving one of the devices into CMOS latchup.  This case
> can have all sorts of hard to diagnose symptoms because it may not hit the
> part of the silicon die that you would expect...   Take a look at the spec
> sheet for the output levels on both boards and make sure they are
> compatible.  RS-232 levels direct driving a embedded processor or controller
> or anything expecting TTL is not a good thing.
>
> -Hope this helps give you a direction to investigate.

Each of the lines is ostensibly running through a RS-232
Driver/Receiver, as appropriate.  The symptom I think I should work on
right now is the power issue: with no signal lines connected, the
servo controller has problems if the line converter is powered.  I
doubt interfacing problems can travel across a 3" airgap, but I'll
keep that in mind for when it still doesn't work after both pieces are
turned on at the same time.

  -- Eric

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