> Okay, I have more data on the full system, and more data on what's
> causing the problem.   Crude diagram attached.
>=20
> The power conditioner has filtering caps, reverse protection, etc but I d=
on't
> know the specifics.  I do know that B draws approx 160mA, and C draws
> approx 65mA.  C is the device of interest here... the one with the EEPROM
> getting corrupt.  C also has another ground for a motor controller.
>=20
> C communicates with one device by  TTL-level data and another by RS232
> signals.  However, there is also another serial interface to a laptop.
> The signals are TTL-level out of the box, but are converted to RS232 by a=
n
> external adapter.
>=20
> Here's the enlightening info... apparently the EEPROM corruption seems to
> be linked to disconnecting & connecting the TTL-to-RS232 adapter board (t=
he
> D-E connection in the diagram).  The protocol for the laptop telling C to
> update certain parameters (changing some EEPROM values) is pretty basic -=
-
> a 1-byte command, a 2-byte parameter value (correlates to a specific
> EEPROM address), and a 1-byte value to update.  I'm wondering if plugging=
 in
> the D-E connection is causing either a surge on the power line (as the TT=
L-to-
> RS232 interface uses 5V provided by C), or perhaps the connection causes =
a
> "switch-bounce" type effect that sends random pulses when being plugging
> in, with some of those pulses being interpreted as commands to update
> parameters.  Data rate is 19200.
>=20
> For a test I can disable the EEPROM-write mechanism in C (so I'd receive =
the
> command, but do nothing) and see if that stops the problem.  If so, I can=
 add
> checksums etc to that protocol.
>=20
> Yes, I should still find out how much filtering is in the system, and add=
 to C if
> more is needed, but thinking that may not be this specific issue now.
>=20
> But does this provide any other clues?  Mark Jordan mentioned ground loop=
s,
> so I'm wondering if the secondary ground to C may be causing some of that=
..

That would certainly be a concern, but I would also wonder why device A is =
not fed from the output side of the power conditioner instead of the input =
side. The possibility of noise then being injected into device C via the gr=
ound of the Rs232 link between A and C should not be overlooked.


--=20
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