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Re: RS-485 port using on ETRAX LX and RS-485-to-RS232 converter by Moxa...




----- Original Message -----
From: "Vladimir Bormotov" <bor@xxxxxxx.ua>
Cc: <dev-etrax@xxxxxxx.com>
Sent: den 9 december 2002 12:19
Subject: Re: RS-485 port using on ETRAX LX and RS-485-to-RS232 converter by
Moxa...


>
> Hi, johan!
>
> >>>>> "ja" == johan adolfsson <johan.adolfsson@xxxxxxx.com> writes:
>
> >>   We have some troubles with connection rs-232 device via Moxa A52
Smart
> >>   Converter to devboard's rs485 port.  Programm inside DevBoard can't
> >>   get valid data from rs-232 device, behinde conerter.  In other side,
> >>   Moxa A50 converter work perfect.
> >>
> >>   programm use /dev/ttyS3 device as serial device, set speed, baudrate,
> >>   parity..
>
> >>   can anyone comment this?  any solutions?
>
>  ja> Hi, I assume you are using 2-wire RS-485.
>
>  4-wire rs-422.
>
>
>  ja> Are you controlling the RTS signal from the DevBoard program manually
>  ja> or using the RS-485 ioctl() to configure RS-485 (TIOCSERSETRS485) and
>  ja> write RS-485 data using the TIOCSERWRRS485 ioctl()?
>
>  ja> The RTS signal controls the direction of the RS-485 line so you must
>  ja> do something with it.  You must use kernel 2.4.19 with the patches
>  ja> from http://developer.axis.com/download/linux/ for RS-485 to work.
>
>  no, we don't use any rs-422/485 specific IOCTLs.  /dev/ttyS3 used as
>  simple rs-232 port.
>
>
>  ja> For 2-wire RS-485 it is the RX pins that should be used, they can
>  ja> switch direction (with RTS), but the TX pins are always transmit.
>
>  ok, we try 2-wire connection..
>
> --
> Bor.

Hmm... if you use 4-wire I can't think of any reason why it shouldn't
work unless you do something with the RTS signal.
I don't have any experiance with the Moxa A52, but perhaps you need to
hardwire the RTS and CTS signals on the A52?
Or could there be a wiring problem or the need for biasing on the
RX lines?

/Johan