>rs232 isn't spec'ed for 500m of cable.  IIRC, it has specs like:
>1) maximum speed 19200
>2) 19200 has a cable length limit of about 20 feet.
>3) "HW flow control" doesn't exist.

I guess RTS control of a multidrop modem isn't flow control? CTS says the
link is ready to accept.

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