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OK, I'll chime in here. This really doesn't need to be as complicated as everyone's making it seem. No, absolutely not! In that post, you provided VB.NET code with this line: regvals = ModC.ReadHoldingRegisters(0, 10) This is reading Modbus register addresses 0 to 9, or in hexadecimal, 0x000...

What is the other document that you reference here that has the 0x55 0x55 0x01 0xD0 0x01 0x00 0xF0 packet that works with your equipment? Can you provide the manufacturer and model of the controller?

OK, so you are able to get a successful response from device when sending 0x55 0x55 0x01 0xD0 0x01 0x00 0xF0. What do each of the bytes mean in this packet? It doesn't seem to use the same CRC, as calculating the CRC on 0x55 0x55 0x01 0xD0 0x01 gives 0x00D0, not 0x00F0. Does the device respond...

I calculated the CRC on the bytes 0x16 0x16 0x01 0xFF and got 0x5CA4, therefore, I think your entire packet should be 0x16 0x16 0x01 0xFF 0x5C 0xA4. I believe you may have had the CRC bytes reversed. Also, please make sure that the PC software you're using is configured to send hexadecimal bytes...

Since the SEALEVEL 7205ec is a RS-232, RS-422, RS-485 serial interface card, I'll assume you're using Modbus RTU. And since you only mention the SEALEVEL 7205ec and ModScan23, I'll also assume you are trying to communicate from a computer using some type of adapter (USB to RS-232 or USB to...

It's impossible to help given the limited information you've shared. How is the CRC calculated? Does the device use hardware handshaking signals? What are you using to communicate to it PC software? What communication settings (baud rate, data bits, parity, stop bits) are you using? Can you...

Interesting, it does seem like this device is not formulating its exception responses properly, as they are missing the CRC. Of course, this is an invalid packet, so it depends on how each master would handle invalid responses. It seems the library you're using simply discards the invalid...

An exception response for a Modbus RTU slave should be 4 bytes in length. Regardless, exception code 01 is Illegal Function, meaning the device doesn't support the Read Device Identification command. Are you able to read registers using Function Code 03? Note that the register addresses in the...

Just to confirm, you meant greater than here instead of less than, correct? The spec states that if a silent interval of more than 1.5 character times occurs during a frame transmission, the frame is deemed an incomplete message and should be ignored. Yes, if the master's request is violating...

A timeout, by definition, is the master waiting for a response after sending a request (i.e. not transmitting anything more on the bus) and not receiving a response after a given amount of time (typically in the hundreds of milliseconds range). The 3.5 char time is far smaller than the timeout...

If you were strictly following Figure 30 in the spec (though we both agree seems backwards), that would dictate that exception code 02 Illegal Data Address be returned for your example #7, since the state diagram shows the Object ID being checked first. However, my opinion is that it makes more...

I think if most any installation scrutinized an RS-485 bus (outside of lab conditions) to this level, you would find occasional errors. Although RS-485 is quote robust, allowing long cable runs and minimizing the impact of external noise and interference, it's not a perfect system. Of course...

I interpret the spec as saying, for any stream access the following is applicable: My interpretations is that the exception code response is only for individual access: Keep in mind that the spec defines the 3 categories in an additive nature, i.e.. Regular data objects include Basic data...

OK, am I understanding correctly that you've resolved your issue then? The problem was that you had two masters connected to the RS-485 bus at the same time. When you disconnect the other master, Modbus Poll can successfully communicate to the slave device. Is this correct?

Please clarify. Did you reconfigure the EuroAir device from being a master to a slave and now everything is working as expected or are you simply saying that the EuroAir device is a slave? Are there any other devices or equipment connected to this RS-485 network?

This is almost assuredly not an issue with this device not implementing Modbus correctly. The device does seem to use standard Modbus. The confusion probably comes from the fact that this vendor's documentation only shows the Modbus PDU instead of the entire ADU (refer to page 3 of the spec...

A checksum error could be caused by incorrect wiring or incorrect communication settings. How do you have the devices wired together? Keep in mind that notations such as "A" and "B" are not standardized amongst vendors, so you may need to swap your A and B connections at one device. If the...

I don't think the spec is necessarily wrong, you may just not be interpreting it the way it was intended. The line in question is 3. Shift the CRC register one bit to the right (toward the LSB), zero–filling the MSB. Extract and examine the LSB. The intended interpretation of the above is that...

I'm not familiar with the term Profile GSD file, but when I used the term device-specific GSD file, I simply meant that every device has its own GSD file. For example, for your specific device, I believe you should use the "PROFIBUS GSD file - pH/ORP Converter FLXA21" GSD file available under...

First, I recommend trying to confirm what SAIA technical support told you is actually true (in my experience, communication is frequently a less important feature of devices and sometimes manufacturers' technical support staff may not actually know how their product communicates - there may only...