Citect v7.40 SP2 - Modbus/TCP - Request wrong Word count

agoslinski said:

Hello

I am trying to connect my Citect SCADA with power meter ASTec PRO380-Mod which is connected to my BMS network via MOXA MGate MB3170.
My problem is that when I lookup the packets send to Moxa with Wireshark or MGate Manager I can see that:

1. Citect sends request for register 4128 that I configured in citect.ini to check if power meter is available in network.

--citect.ini--
MODNET.PORT74_BOARD1.ASTec
- FloatMode = 1
- InitVar = 4128
- InitVarType = 3

--Modbus request--
[02 03 10 20 00 01 81 33]

2. Moxa sends the response with value 25 80 HEX = 9600 DEC under register 4128 (baudrate)

--Modbus response--
[02 03 02 25 80 E7 74]

3. Citect sends request for register 8200 (Real Voltage phase 1) which is my first variable configured in Equipment editor.

--Modbus request--
[02 03 20 08 00 7A 4E 18]

As You can see Citect sends request with Word Count = 122 (7A HEX) and it should be 2 (2 words = 4 bytes = 1 REAL value)

Moxa is unable to response to such request and after some time Citect starts to send request from the beginning (4128)

After bed request In Wireshark I can see packets such as:
TCP Dup ACK
TCP Keep-Alive ACK
RST

I did not have such problems using Modbus Poll program (modbustools com).

In attachment You can find screenshots from Wireshark and MGate Manager.

Could You please help me with my problem.

Best regards

Click to expand...

agoslinski said:

I think I know what's wrong.

Using Wireshark I checked other Modbus/tcp devices in my network.
It seems that Citect sends one request for all (or some part of) variables defined, it looks up lowest and highest register and sends request from the lowest register with appropriate value of Word count to get all registers from lowest to highest.

I think that my power meter is not able to send back such big response. How can I limit amount of registers in one request?

Click to expand...