Re: serial communication problems

Gerald Emig
2002-05-29T14:07:17Z

On Wed, 29 May 2002, Deepak Gupta wrote:

> Hi,
>
> I have a strange problem with the serial line communication in Linux
> (RH 7.2, kernel 2.4.7-10). We have some electronic locks that are
> controlled by a PC. The locks are connected by a RS485 twisted pair
> (multidrop) and this line terminates in a 485-232 converter box which
> is connected via the serial line to a PC. The lock vendor has supplied
> a Windows software to program the locks which works fine on this PC.
> He has also given me the protocol that is followed between the PCs and
> the locks. I am trying to write my own Linux based software for
> programming the locks.
>
> The problem is that when the vendor software sends a command to a lock
> it replies obediently but when my program writes exactly the same sequence
> of bytes to the serial line, I don't get a response (the protocol
> says that the lock will not respond unless it gets a valid command).
> I know the locks use 9600 baud, 8 bits, no parity, 1 stop bit and I
> am using the same. I also tried with and without hardware flow control
> (RTS/CTS) but no luck. I know that the command I send is right since
> I used another PC to listen to what the vendor software writes on the
> serial line and it matches the protocol description that I have.
>
> Incidentally I opened up the 232-485 converter box and saw that it
> uses only the TX, RX, SG, RTS and CTS lines on the RS232 side. So
> it cannot be a matter of DTR or some other signal.
>

I had a similar problem a few days ago.
Old software worked, new one did not.
So I also used a third PC to look what the others talk.
I noticed the same as you.

Solution was that RTS had to be set active.

> Please help.
>
> Deepak Gupta
> -
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