I have a testing environment for the modbus. I have the Beckhoff CX5140 with EL4004. Then I have netbiter IOX-8AIV connect to EL4004. Then from my laptop, I use type C to Serial modbus RTU RS485 to connect to netbiter. when I run the Modscan 64 bit, it return Checksum Error in response Message.




I try use another modscan software to scan and it return me some result but I not sure what the meaning of the return result. in Beckhoff, I has force the 6v value to the netbiter but seem like nothing change on the return result. In netbiter, I use input 1 & 2.


I'm totally new in this field and no any training before hands on for this job.

 

Since the Netbiter IOX has only a single RS-485 port, I'm assuming you have both the Beckhoff and your computer connected to the IOX's single RS-485 port and communicating at the same time. Modbus RTU allows only one master to be on the network. Both the Beckhoff and your computer running ModScan are Modbus RTU masters. Try disconnecting the Beckhoff and see if the checksum errors go away in ModScan.

 

Hi @jschulze , thanks for the reply. May I know how I can know Netbiter IOX only single RS-485 port? I'm totally new in the industry and no any knowledge and need learn from basic.

 

How many terminal blocks does the Netbiter IOX have with RS-485 signals (labeled A and B)? I believe it only has one, therefore it has only one RS-485 port.

 

Ya, it only have one A and B. I try to disconnect Beckhoff connection from NetBiter Input 1 and 2. And only left my laptop connect to the Netbiter. I run the modscan but it still giv eme the same error. Any configure or cabling I make wrong?

 

Try swapping your A and B wires (with some vendors A is positive and B is negative, but for others, B is positive and A is negative).

If your USB to RS-485 adapter has a ground terminal, connect it to the Netbiter's ground terminal in addition to the A and B wires (3 wires total).

Double check that your baud rate, parity, stop bits, and slave address (ID) match both on the Netbiter and in ModScan.

 

May I know how to check the slave Id? 0v is equal ground?

 

Slave ID is labeled "Device ID" in ModScan and it is set via dip switches on the Netbiter (refer to the manual for details https://www.netbiter.com/docs/default-source/netbiter-english/manuals/hms-hmsi-27-228.pdf)

Yes, 0V is equivalent to ground.

 

I have connect the ground from my USB to RS485 to the netbiter ground. The node Id set to 2, the baud rate use default which is 9600, data bits is 8, stop bits 1 and parity None. In my USB to RS485 adapter, it also set the same. And in the modscan64, i set the same. But it give me the same error message. May I know, if it is success, what will show in the result? 40002 will show the voltage value?

 

When communications is successful, ModScan's Polls and Responses counters will increment together and there will be no messages in red text at the top.

As for which registers to access on the Netbiter, refer to page 32 in the manual I linked in my previous response. Analog Input 1 is register 30002 (which is another way of saying Input Register 2).

Do you receive the same checksum error in ModScan if you power off the Netbiter or disconnect the RS-485 wires from the Netbiter?

 

If I turn off the netbiter, the modscan show me "Received invalid response to modbus query"

 

If I turn off the netbiter, the modscan show me "Received invalid response to modbus query". May I know, if I swap the A and B, netbiter and my USb to RS485 both also need to swap? Or I only swap in NetBiter?
It is the connection correct if I swap A and B

 

What error message does ModScan show if you disconnect the RS-485 wires?

If it doesn't show a timeout error, there may be an issue with your USB to RS-485 adapter. You may need to try a different adapter.

When you swap the A and B wires, it should be done at one end only.

The Netbiter does have RS-485 RX and TX status indicators (LEDs). The RX LED should flash when it receives requests from ModScan and the TX LED should flash if it sends a response. Are you seeing both of these LEDs flash when you're RS-485 wiring is connected and Modscan is sending requests?

 

If I turn off the netbiter, the modscan show me "Received invalid response to modbus query" and then "Modbus Message Timeout"
The TX and RX LED both flash and the Tx and Rx Led in USB to RS485 adapter also flash when it is connected.

 

I have swap A and B in netbiter side, when run the modscan; it show me "Received invalid response to modbus query" and then "Modbus Message Timeout" It's that means Netbiter A = positive and B = negative?

 

If swapping your A and B wires results in the same behavior as when the Netbiter is off or when the RS-485 wires are disconnected, then it is very likely the wrong polarity and you should swap the wires back.

You should not be receiving a "Received invalid response to modbus query" when the Netbiter is off or the RS-485 wires are disconnected. It appears your USB to RS-485 adapter has RxD+, RxD-, TxD+, and TxD- signals and you have jumper wires connected between the RxD+/TxD+ and the RxD-/TxD- signals. If you disconnect all wires from your USB to RS-485 adapter, including the jumper wires, do you still see a "Received invalid response to modbus query" error in ModScan or does it only show "Modbus Message Timeout".

If the "Received invalid response to modbus query" error goes away when removing the jumper wires on your USB to RS-485 adapter, it seems that the adapter may be receiving its own transmission and this may be what is causing the issues you're seeing. Can you provide documentation, or at least the vendor and model, of the USB to RS-485 adapter you're using? Can you try a different USB to RS-485 adapter?

 

Here is the user manual for the Type C to RS485 adapter. It is from Dtech ftdi.

 

Thank you for the USB to RS-485 adapter documentation. According to that documentation, you do not need to connect jumper wires to the adapter. Refer to the image under 6. Connection instructions->Type-C TO RS485->2. RS485 point-to-more/ half duplex 2-line communication. You should have wires connected to T/R+ (DB9 pin 1), T/R- (DB9 pin 2), and GND (DB9 pin 5).

Unfortunately that document is not clear whether you need to manually configure the adapter's mode to 2-wire mode versus 4-wire mode somehow (perhaps in the adapter properties in Device Manager) or if it automatically detects the mode.

Please try removing the jumper wires you have connected to your adapter to see if that resolves the issue you're seeing.

 

Hi @jschulze , means I just need one wire from Rx+(adapter) to Rx+(netBiter) then Rx- to Rx-. The Tx+/- no need wire, right?

 

I believe these are the only connections you need to make:

Dtech Adapter	Netbiter
T/R+ (DB9 pin 1)	A
T/R- (DB9 pin 2)	B
GND (DB9 pin 5)	GND (VDC-)

No wires need to be connected to RXD+ (DB9 pin 3) and RXD- (DB9 pin4) on the Dtech adapter.