Dave Liquorice  wrote:
> On Mon, 8 Jan 2018 20:34:17 +0000 (UTC), Kiwi User wrote:
>
>> A different make of USB-serial converter?
>
> Worth a try, I had a PL2303 based convertor connected to an APC UPS.
> Every so often the adpater would disconnect from the USB and
> reconnect breaking the UPS Tools monitoring...
>
> Got a FTDI FT232L based convertor and not had a sniff of the problem
> since.
>
> Curiously I still have 3 of the same PL2303 adpaters in use with
> other devices without a hitch. Yes, I did try some of those with the
> UPS and they also failed in the same way.
>

It looks as if the problem is solved. The fix was to add pulldown resistors
to ground from the PL2303's rx and tx pins. It now seems to work with the
ttl-rs232 level shifter down to 1200 baud. At 300 baud about one character
in ten is garbled. At 110 baud the loopback test fails completely, but that's
ok 8-)

Perhaps the same fix would help with your UPS.

Thanks for reading,

bob prohaska

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