Citect talking MODBUS RTU to Advantech ADAM 4024


Thread Starter

Bryant Chin

Good day fellow engineers,

I am new to Citect and the world of automation. Been tasked to work with Advantech ADAM 4024 I/O modules. It has 4 digital Inputs and 4 analog outputs. I am able to poll from CitectSCADA for the 4 analog outputs with no issue, but the polling of the 4 digital inputs always returns a #BAD comment.

I did abit of digging with putty application, to sniff for the MODBUS request and response package. It seems that Citect is requesting for a 2bytes responses. Because the ADAM 4024 only have 4 digital input that corresponds to a 8bits, the response with an exception code #1.

I also tried using MODScan to request for the 4digital inputs of ADAM 4024. I was successful in doing so as I can dictate the number of registers to read, in the ADAM 4024 cases is 4.

Has anyone ever encountered or overcome this similar issue with ADAM I/O module? Any sharing of your experience will with be valued. Thank you very much.

I recently installed the ADAM-6050 18Ch digital Input/Output with Citect 7.3. The MODNET3 driver was used to communicate via ethernet and I also had to add the [MODNET]RegisterBitReverse=1 to citect.ini file to reverse the 16 bits.

The addressing for physical inputs was DI0 on ADAM-6050 and Citect tag was 00000, DI1 = 00001 and so on.

Hope this helps.

Lynn August Kinse

Yah, this is an unfortunate result of tunnel-vision or naivety, which is common in the Modbus world. For example, a device has 13 words of data so they answer a poll for 13, but not 125 (or even 14) words.

My opinion is that any slave SHOULD answer any request which BEGINS in a valid data region, appending either 0x0000 or 0xFFFF to the data to create a valid response. This forcing customers to probe & guess the perfect number satisfies no one.

So in the case of your device with 4 bits only, I'd suggest that they answer any request for 4, 8, 16, 32, or even 2000 bits - if it begins in a valid data region. The supplier (Advantech) is obviously either not experienced in modbus or arrogantly naive. Considering I own many Adventech product which are many years old, I guess that means they are arrogantly naive.
Thank you for your reply. I have got myself a ADAM 4055 8DI & 8DO and that works fine. Unfortunately, I have chucked the ADAM 4024 aside. :D
Hello Lynn,

Thank you very much for your reply. now I do know that I am not the only one experiencing this difficulty with advantech I/O modules :D cheers