Twido Slave Modbus connection testing?

Hello everybody!

I am having an issue I'm hoping someone here can help me with. I have a TWDLCAA24DRF plc which I have configured to act as a slave in MODBUS RTU communication. What I want to do is test the modbus connection via a TSXCUSB485 RS485 to usb converter.
I have downloaded the trial for Modbus Poll off of internet and I am trying to connect the PC (as a master) to the PLC (as slave) just to see if I can write a word from the PC to the PLC via Modbus.

I have turned the switch on the converter into position 3 (Other Direct) which, I suppose, connects pin 5 to 0V, so that the controller knows the connection is no longer a programming connection. However whenever i am attempting to connect to the controller in Modbus Poll I keep getting Timeout error.

The cable is connected int port no1 of the controller and the connection settings are:
Baud :19200
Data Bits: 8 (RTU)
Parity :none (recommended for port 1)
Stop bit: 1
Response timeout 1 sec
Time between frames 10 ms

Since the controller is a slave i Have set the adress of the port to 2.

Could anyone help me figure out what I'm doing wrong, or are there other Modbus master PC emulating programs which i could use that are easier to comprehend?

Thank you!

International language

http://www.youtube.com/watch?v=29xxfOyv-g8

http://www.youtube.com/watch?v=5nT3LEeIIbU

I don't understand

My suggestions for RS-485 are
- what virtual COM port is the USB-485 converter installed on? Is that the COM port you've selected in Modbus Poll? The COM port is shown in Windows Device Manager under Ports (COM & LPT).

- The 485 is probably 2 wire. Have you tried swapping the leads at one end? The labeling of A and B lines (or + and -) is not consistent between manufacturers. Although A should connect to A, sometimes A connects to B.

With Modbus in general, it's my experience that I'll never try to write until I can read a unique value (something other than zero) from a register. Getting a valid read of a known, confirmable value tells you the com link is working, and that you have the correct register, not one on before or after it.

Can you read values with Modbus Poll?

I'm not sure Modscan32 is any easier to use than Modbus Poll, but since I'm used to Modscan, I can set it up quickly. It runs for only 5 minutes before timing out in the trial mode, but can be restarted immediately.