Well, now I know it's not a voltage problem. I actually used the scope to
analyze over a working rs485 (with modbus) connection and the levels and the
signals are exactly the same.
What brings me to think the problem is that the driver (or maybe de library,
anybody knows?) isn't waiting for the slave response.
In the working rs485 I had the problem that first the usb-rs485 was confused by
the system (win xp machine) as a usb-rs232 cable, and even it send correctly
the signal, I couldn't get any answer. But after installing the correct driver,
the communication start working really smooth.
So I guess in some part, the embedded is not waiting for the response of the
slave.
Any ideas?
--- In "akikem" <> wrote:
>
> Greetings,
> I have been working with a TS-7400 with ENC-420 trying to use the RS485 port.
> I am using the Linux Kernel of the WifiBox (2.6.29) along with the
> tsuart7400.ko module. When I load it a /dev/ttts0 is created.
> In the other hand I am using the libmodbus 2.0.3. The code I create is
> simple, I configure the port to use RTU, 9600,8,N,1, then I open the modbus
> connection, after that I use function 3 to ask for a register. Then I close
> the connection.
> I have here several Modbus RTU devices, an HTS, and a Voltage analyzer. But
> when I connect any of them, I get a timeout response. I am sure about the
> address I am calling, and actually, the device shows that there is an attempt
> of communication.
> When I check the signal with the scope, I can clearly see the signals in X+
> and X-, however, the signals go from +5Volts to 0V, when the standard states
> +12 to -7. I guess this is the reason why the slaves aren't answering at all,
> but I don't know why the ttts0 is sending this levels.
> Hope someone could light me a little..
> Thanks!
> Enrique
>
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